ci: fix version comment inconsistencies

- zizmor.yml: align checkout comment to `# v6` matching other workflows
- ci.yml: fix actions/cache comment from `# v5` to `# v5.0.4` (actual tag)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wochinge

.github/workflows/ci.yml

@@ -46,7 +46,7 @@ jobs:
           version: "0.11.2"
           python-version: "3.13"
           enable-cache: true # zizmor: ignore[cache-poisoning] CI-only, no artifacts published
-      - uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5 # zizmor: ignore[cache-poisoning]
+      - uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4 # zizmor: ignore[cache-poisoning]
         name: Cache mypy cache
         with:
           path: ./.mypy_cache

.github/workflows/zizmor.yml

@@ -23,7 +23,7 @@ jobs:
       contents: read
     steps:
       - name: Checkout
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           persist-credentials: false
       - name: Run zizmor