[9.3.0] Close the coverage post-processing `FileOutErr` before deleting its files

[bazel-io]

Forked from #30662

[bazel-io]

Cherry-pick was attempted but there were merge conflicts in the following file(s). Please resolve manually.

src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java

cc: @bazelbuild/triage

[iancha1992]

Cherry-picked in #30678