ci: Don't run toolchain-test in non-envoy repos (#40998)

Back port #40996 to 1.35

Signed-off-by: Ted Poole <[email protected]>

Author: tedjpoole

.github/workflows/toolchain-test.yml

@@ -16,6 +16,7 @@ concurrency:
 jobs:
   toolchain-test:
     runs-on: ubuntu-22.04
+    if: github.repository == 'envoyproxy/envoy'
     strategy:
       fail-fast: false
       matrix: