chore(ci): run macOS jobs in GitLab for MergeQueue. Remove broken label rule (#1833)

# What does this PR do?

Now that we have dedicated MacOS runners (DataDog/libddprof-build#166) in GitLab, contention with the general pool is not an issue. We should be running the MacOS tests on the MergeQueue to prevent bad mac merges to main. 

Using the `run-macos-tests` label in Github to trigger the jobs in GitLab for PRs didn't (ever?) work. So just getting rid of it. Assuming things work out well with the dedicated runners we can consider upping the allocation of runners and just running macOS builds on all PRs.

# Motivation

What inspired you to submit this pull request?

# Additional Notes

Anything else we should know when reviewing?

# How to test the change?

Describe here in detail how the change can be validated.


Co-authored-by: edmund.kump <edmund.kump@datadoghq.com>

Author: ekump

.gitlab-ci.yml

@@ -28,11 +28,11 @@ trigger_internal_build:
       when: always
     - if: '$CI_EXTERNAL_PULL_REQUEST_SOURCE_BRANCH_NAME =~ /^release\//'
       when: always
-    - if: '$CI_MERGE_REQUEST_LABELS =~ /run-macos-tests/'
+    - if: '$CI_COMMIT_BRANCH == "main"'
       variables:
         LIBDATADOG_ENABLE_MACOS_JOBS: "true"
       when: always
-    - if: '$CI_COMMIT_BRANCH == "main"'
+    - if: '$CI_COMMIT_BRANCH =~ /^mq-working-branch-/'
       variables:
         LIBDATADOG_ENABLE_MACOS_JOBS: "true"
       when: always