chore(ci): correct actions/cache version comment to v5.0.5

The actions/cache step pinned commit 27d5ce7 (= tag v5.0.5) but the
trailing comment read "# v5". The v5 moving tag points to a different
commit, so the comment was untruthful and zizmor flagged it as
ref-version-mismatch. Update the comment to the exact version the SHA
resolves to, matching the exact-version pin convention used elsewhere
(e.g. actions/checkout # v6.0.3).

Resolves code-scanning alert #2552

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/pre-commit.yml

@@ -63,7 +63,7 @@ jobs:
           yarn install --immutable
 
       - name: Cache pre-commit environments
-        uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5
+        uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
         with:
           path: ~/.cache/pre-commit
           key: pre-commit-v2-${{ runner.os }}-py${{ matrix.python-version }}-${{ hashFiles('.pre-commit-config.yaml') }}