bazel/ci: Fix arm cache/download issue (#39684)

Currently arm still gets errors about downloading icu etc (been better
recently) - whereas its fixed in x86

this makes the caching for arm closer to x86 - and should resolve issues
like this where its missing required cache for ci

Signed-off-by: Ryan Northey <[email protected]>

Author: phlax

.github/workflows/_request_cache.yml

@@ -84,3 +84,5 @@ jobs:
              --config=cache-envoy-engflow
           targets: >-
             //test/...
+            //contrib/...
+            //source/...