Use the correct variable name in kokoro/create_github_release_branch.sh

PiperOrigin-RevId: 542488584
Change-Id: Id9c9c3fa9a31fd537e9dbf3d0e3e7cf4f57046b6

Author: morambro

kokoro/create_github_release_branch.sh

@@ -47,9 +47,9 @@ fi
 
 GITHUB_RELEASE_UTIL_OPTS=()
 if [[ "${IS_KOKORO}" == "true" ]] ; then
-  # Note: KOKORO_GIT_COMMIT is populated by Kokoro.
+  # Note: KOKORO_GIT_COMMIT_tink_go_awskms is populated by Kokoro.
   GITHUB_RELEASE_UTIL_OPTS+=(
-    -c "${KOKORO_GIT_COMMIT}"
+    -c "${KOKORO_GIT_COMMIT_tink_go_awskms}"
     -t "${GITHUB_ACCESS_TOKEN}"
   )
 fi