ci: bump deprecated actions/checkout and actions/cache to v4 in lint-code

GitHub started auto-failing workflows using actions/cache@v2 in
December 2025 (deprecation notice). actions/checkout@v2 is in the
same bucket. With this PR removing the 'branches: [main]' filter on
pr.yml, the lint-code job now runs on every PR — so the red-flag
deprecation caught by the runner causes every new PR to fail until
these two pins are rotated forward.

Minimal change: v2 → v4 on both uses: lines; everything else in the
job stays the same.

Signed-off-by: yuriyryabikov <22548029+kurok@users.noreply.github.com>

Author: kurok

.github/workflows/pr.yml

@@ -7,9 +7,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Cache dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: '**/node_modules'
           key: ec2-github-runner-${{ hashFiles('**/package-lock.json') }}