Signed-off-by: Sebastiaan van Stijn <[email protected]>

ci: update actions and test against "oldest", "oldstable" and "stable"

`Pattern.compile` was updating `Pattern.matchType` in-place. In situations where
the resulting regex failed to compile, it would return early (with an error),
but the `matchType` was already set.

In that situation, `Pattern.match` would consider the `matchType` already
set, skip the `p.matchType == unknownMatch` condition, and fall through
to trying to use `p.regex`, which was nil, and resulted in a panic;

```
journalctl -u docker.service -f
dockerd[423967]: panic: runtime error: invalid memory address or nil pointer dereference
dockerd[423967]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x90 pc=0x557e0f7ebf80]
dockerd[423967]: goroutine 1241 [running]:
dockerd[423967]: regexp.(*Regexp).doExecute(0x557e11b285a0?, {0x0?, 0x0?}, {0x0?, 0x557e11922650?, 0x557e11922650?}, {0xc0009d3db0?, 0xc000061778?}, 0x557e0f6d0d99?, 0x0, ...)
dockerd[423967]:         /usr/local/go/src/regexp/exec.go:527 +0x80
dockerd[423967]: regexp.(*Regexp).doMatch(...)
dockerd[423967]:         /usr/local/go/src/regexp/exec.go:514
dockerd[423967]: regexp.(*Regexp).MatchString(...)
dockerd[423967]:         /usr/local/go/src/regexp/regexp.go:527
dockerd[423967]: github.com/moby/patternmatcher.(*Pattern).match(0x557e11922650?, {0xc0009d3db0, 0x1})
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/patternmatcher/patternmatcher.go:334 +0x26b
dockerd[423967]: github.com/moby/patternmatcher.(*PatternMatcher).MatchesOrParentMatches(0xc000d761e0, {0xc0009d3db0, 0x1})
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/patternmatcher/patternmatcher.go:142 +0xda
dockerd[423967]: github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb.validateCopySourcePath({0xc0009d3db0, 0x1}, 0xc0000621f8)
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb/convert.go:2023 +0x55
dockerd[423967]: github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb.dispatchCopy(_, {{{0xc0009d3dc0, 0x1}, {0xc0009b5d10, 0x1, 0x1}, {0x0, 0x0, 0x0}}, {0x0, ...}, ...})
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb/convert.go:1607 +0xd5c
dockerd[423967]: github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb.dispatch(_, {{_, _}, {_, _, _}, _}, {0xc000aab6a0, {0x557e1214c560, 0xc0007b79e0}, ...})
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb/convert.go:1004 +0xafb
dockerd[423967]: github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb.toDispatchState({_, _}, {_, _, _}, {{0xc000d5c8d0, {0x0, 0x0}, {0x0, 0x0}, ...}, ...})
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb/convert.go:731 +0x3926
dockerd[423967]: github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb.Dockerfile2LLB({_, _}, {_, _, _}, {{0xc000d5c8d0, {0x0, 0x0}, {0x0, 0x0}, ...}, ...})
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb/convert.go:90 +0x65
dockerd[423967]: github.com/moby/buildkit/frontend/dockerfile/builder.Build.func6({0x557e121613e0, 0xc000cfd590}, 0x0, 0x557e0f64accb?)
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/buildkit/frontend/dockerfile/builder/build.go:136 +0xfe
dockerd[423967]: github.com/moby/buildkit/frontend/dockerui.(*Client).Build.func1()
dockerd[423967]:         /root/build-deb/engine/vendor/github.com/moby/buildkit/frontend/dockerui/build.go:39 +0x71
dockerd[423967]: golang.org/x/sync/errgroup.(*Group).Go.func1()
dockerd[423967]:         /root/build-deb/engine/vendor/golang.org/x/sync/errgroup/errgroup.go:93 +0x50
dockerd[423967]: created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 1136
dockerd[423967]:         /root/build-deb/engine/vendor/golang.org/x/sync/errgroup/errgroup.go:78 +0x95
systemd[1]: docker.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
systemd[1]: docker.service: Failed with result 'exit-code'.
```

This patch:

- updates `Pattern.compile` to use a local variable for the intermediate
  state, and only updates `Pattern.matchType` when completing successfully.
- adds a nil-check in `Pattern.match` as defense-in-depth.

Signed-off-by: Sebastiaan van Stijn <[email protected]>

fix panic /  nil pointer dereference on invalid patterns