* chore(ci): fix typo in restrict presubmit samples ITs to only snapshot

Fixes below error in Java repos when googleapis/synthtool#804 was merged:
```
github/java-bigquerystorage/.kokoro/build.sh: line 81: pushd: {SAMPLES_DIR}: No such file or directory
```

Thanks @kolea2 for spotting this in Fusion build logs.

cc @chingor13

Source-Author: Stephanie Wang <[email protected]>
Source-Date: Mon Oct 26 13:44:04 2020 -0400
Source-Repo: googleapis/synthtool
Source-Sha: f68649c5f26bcff6817c6d21e90dac0fc71fef8e
Source-Link: googleapis/synthtool@f68649c

* chore(java): enable generated-files-bot

This bot will comment on pull requests that modify templated files. For java, we configure to read from our 2 synth.metadata files: (primary templates and README)

Source-Author: Jeff Ching <[email protected]>
Source-Date: Fri Oct 30 14:22:02 2020 -0700
Source-Repo: googleapis/synthtool
Source-Sha: b19b401571e77192f8dd38eab5fb2300a0de9324
Source-Link: googleapis/synthtool@b19b401

🤖 I have created a release \*beep\* \*boop\* 
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### Updating meta-information for bleeding-edge SNAPSHOT release.
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