bug: flaky race condition test in hooks_test.go (issue #768 regression)

[zeroedin]

Problem

The test Hooks > Race safety (issue #768) > batch goroutine receives a stable input snapshot independent of timeout reassignment at internal/plugin/hooks_test.go:574 fails intermittently under go test -race.

Evidence

Failed in CI on PR #809 (an unrelated docs-only change — moved plugin files and updated config):

Summarizing 1 Failure:
  [FAIL] Hooks Race safety (issue #768) [It] batch goroutine receives a stable input snapshot independent of timeout reassignment
  /home/runner/work/alloy/alloy/internal/plugin/hooks_test.go:574

Ran 214 of 214 Specs in 14.985 seconds
FAIL! -- 213 Passed | 1 Failed | 0 Pending | 0 Skipped

213 of 214 tests passed. The single failure is unrelated to the PR's changes.

Impact

Flaky CI failures block unrelated PRs from merging.

[zeroedin]

Closed in #934