Update GitHub Actions to codecov/codecov-action@v6

This fixes:

> Warning: Node.js 20 actions are deprecated. The following actions are running
> on Node.js 20 and may not work as expected:
> actions/github-script@60a0d83.

Author: TimWolla

.github/workflows/test-suite.yml

@@ -413,7 +413,7 @@ jobs:
         with:
           enableOpcache: true
           jitType: tracing
-      - uses: codecov/codecov-action@v5
+      - uses: codecov/codecov-action@v6
         if: ${{ !cancelled() }}
         with:
           fail_ci_if_error: true