ci: skip tidy in PR CI jobs not dedicated to running tidy

This is both:

1. Redundant, since PR CI has a dedicated `tidy` job
2. A contributor roadblock, because tidy failures block further failures
   from being revealed.

We *only* skip tidy in PR CI and not in Merge CI because tidy in Merge
CI will early-cancel *anyway*.

Author: jieyouxu

src/ci/docker/scripts/stage_2_test_set1.sh

@@ -4,6 +4,16 @@ set -ex
 
 # Run a subset of tests. Used to run tests in parallel in multiple jobs.
 
+# When this job partition is run as part of PR CI, skip tidy to allow revealing more failures. The
+# dedicated `tidy` job failing won't block other PR CI jobs from completing, and so tidy failures
+# shouldn't inhibit revealing other failures in PR CI jobs.
+if [[ -z "${PR_CI_JOB}" ]]; then
+  SKIP_TIDY="--skip tidy"
+else
+  SKIP_TIDY=""
+fi
+
 ../x.py --stage 2 test \
+  "$SKIP_TIDY" \
   --skip compiler \
   --skip src

src/ci/docker/scripts/stage_2_test_set2.sh

@@ -4,7 +4,17 @@ set -ex
 
 # Run a subset of tests. Used to run tests in parallel in multiple jobs.
 
+# When this job partition is run as part of PR CI, skip tidy to allow revealing more failures. The
+# dedicated `tidy` job failing won't block other PR CI jobs from completing, and so tidy failures
+# shouldn't inhibit revealing other failures in PR CI jobs.
+if [[ -z "${PR_CI_JOB}" ]]; then
+  SKIP_TIDY="--skip tidy"
+else
+  SKIP_TIDY=""
+fi
+
 ../x.py --stage 2 test \
+  "$SKIP_TIDY" \
   --skip tests \
   --skip coverage-map \
   --skip coverage-run \