Do not checkout GCC submodule for the tidy job

src/ci/github-actions/jobs.yml

@@ -129,6 +129,10 @@ pr:
   - name: mingw-check-tidy
     continue_on_error: true
     free_disk: false
+    env:
+      # This submodule is expensive to checkout, and it should not be needed for
+      # tidy. This speeds up the PR CI job by ~1 minute.
+      SKIP_SUBMODULES: src/gcc
     <<: *job-linux-4c
   - name: x86_64-gnu-llvm-19
     env:

src/ci/scripts/checkout-submodules.sh

@@ -55,7 +55,11 @@ for i in ${!modules[@]}; do
         bg_pids[${i}]=$!
         continue
     else
+      # Submodule paths contained in SKIP_SUBMODULES (comma-separated list) will not be
+      # checked out.
+      if [ -z "${SKIP_SUBMODULES:-}" ] || [[ ! ",$SKIP_SUBMODULES," = *",$module,"* ]]; then
         use_git="$use_git $module"
+      fi
     fi
 done
 retry sh -c "git submodule deinit -f $use_git && \