ci: skip actions/cache on self-hosted runners (#11986)

cargo registry/target and docker-image caches are already local on a
persistent self-hosted runner; the save/restore pass is pure overhead
(the setup-go cache-save stall on awscli-tests was the same pattern).
Gate every actions/cache step on runner.environment == 'github-hosted'.

Generated with [Devin](https://devin.ai)

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.github/workflows/container_dev.yml

@@ -55,6 +55,7 @@ jobs:
           echo "CFLAGS_aarch64_unknown_linux_musl=-U_FORTIFY_SOURCE" >> "$GITHUB_ENV"
 
       - name: Cache cargo registry and target
+        if: runner.environment == 'github-hosted'
         uses: actions/cache@v6
         with:
           path: |