ci: Fix spurious pipeline failure when deploying a tag to GitHub

Everything succeeds, but because [ -z ${CI_COMMIT_TAG} ] on the last line returns non-zero, it
fails the job.

.gitlab-ci.yml

@@ -291,9 +291,7 @@ push_to_github:
     - echo -e "Host github.com\n\tStrictHostKeyChecking no\n" >> ~/.ssh/config
     - git remote remove github &>/dev/null || true
     - git remote add github git@github.com:espressif/esp-idf.git
-    # Need separate push commands for tag builds and for branch builds
-    - "[ -n \"${CI_COMMIT_TAG}\" ] && git push github ${CI_COMMIT_TAG}"
-    - "[ -z \"${CI_COMMIT_TAG}\" ] && git push github ${CI_COMMIT_SHA}:refs/heads/${CI_COMMIT_REF_NAME}"
+    - tools/ci/push_to_github.sh
 
 deploy_docs:
   stage: host_test

tools/ci/push_to_github.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# gitlab-ci script to push current tested revision (tag or branch) to github
+
+set -ex
+
+if [ -n "${CI_COMMIT_TAG}" ]; then
+    # for tags
+    git push github "${CI_COMMIT_TAG}"
+else
+    # for branches
+    git push github "${CI_COMMIT_SHA}:refs/heads/${CI_COMMIT_REF_NAME}"
+fi
+