ci(e2e): use quoted shell expansion for GINKGO_SKIP

Replace ${{ env.SKIP_E2E }} expression interpolation with quoted
shell variable expansion "$SKIP_E2E" to prevent potential command
injection via the environment variable.

Co-authored-by: Claude <noreply@anthropic.com>

Author: wikkyk

.github/workflows/e2e.yml

@@ -43,7 +43,7 @@ jobs:
         run: echo 'SKIP_E2E=""' >> "$GITHUB_ENV"
 
       - name: Run e2e tests
-        run: "make test-e2e GINKGO_SKIP=${{ env.SKIP_E2E }}"
+        run: make test-e2e "GINKGO_SKIP=$SKIP_E2E"
 
       - name: Upload artifacts
         uses: actions/upload-artifact@v7