This problem generally is due to the required checks do not run or are not triggered on the latest commit of the pull request.
In your case, the three required checks ‘test (macos-latest, 1.14.x)’, ‘test (ubuntu-latest, 1.14.x)’ and ‘test (windows-latest, 1.14.x)’ should be the jobs in the workflow runs related to the pull request.
The workflow runs related to the PR generally include these:
Workflow runs triggered by the events related to the pull request. The events include pull_request, pull_request_review, pull_request_review_comment and pull_request_target.
Workflow runs triggered by push event for the latest commit on the head branch (source branch) of the pull request.
If the three required checks do not run or are not triggered on the latest commit of the pull request. You can navigate to the repository’s Settings > Branches > Branch protection rules. Open the and edit the rules you have set for the master branch. Disable the three required checks.
After changing the rules, refresh or reopen the web page of the pull request, then you can see the three checks disappear from the list of the checks, and you can merge the PR.
To create, edit or delete the rules, you need the owner or the administrator permissions.