GHA runners occasionally experience I/O constraints during root-test
test execution. While concurrent tests rapidly allocate loopback
devices, background udev probing stalls. This quickly exhausts
systemd-udevd's default worker pool ceiling (20 children max), stalling
netlink uevent processing so device-mapper device nodes are never
created for subsequent dm-verity test execution.

Logging cgroups v2 pids.peak telemetry confirmed peak in-flight udev
workers accumulate to 325 during test execution. Raising the
children-max limit to 500 provides comfortable buffer room so udevd
freely spawns worker processes without entering event lockup or causing
test timeouts.

Assisted-by: Antigravity
Signed-off-by: Chris Henzie <[email protected]>