Use CWD for `cache_key` location

After switching to the `workspace_dir` this no longer was valid

PiperOrigin-RevId: 636809886
Change-Id: Ieac255467b3faae2a7eb0bfd62bb98f2fb0921d4
diff --git a/kokoro/testutils/run_bazel_tests.sh b/kokoro/testutils/run_bazel_tests.sh
index 22567bf..14b31b1 100755
--- a/kokoro/testutils/run_bazel_tests.sh
+++ b/kokoro/testutils/run_bazel_tests.sh
@@ -65,7 +65,7 @@
       t) TEST_FLAGS=($(echo "${OPTARG}" | tr ',' '\n')) ;;
       c) CACHE_FLAGS=(
            "--remote_cache=https://storage.googleapis.com/${OPTARG}"
-           "--google_credentials=cache_key"
+           "--google_credentials=$(realpath ./cache_key)"
          );;
       *) usage ;;
     esac