BUG: Add GitHub Action permissions for the labeller
BUG: Add GitHub Action permissions for the labeller

Attempt to enable the pull request labeler to work on forked pull
requests.

Background:

- https://github.com/actions/labeler/issues/12
- https://github.blog/changelog/2021-04-20-github-actions-control-permissions-for-github_token/

richardbeare/ITK,BRAINSia/ITK,thewtex/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,Kitware/ITK,Kitware/ITK,hjmjohnson/ITK,Kitware/ITK,BRAINSia/ITK,Kitware/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,BRAINSia/ITK,Kitware/ITK,hjmjohnson/ITK,thewtex/ITK,BRAINSia/ITK,BRAINSia/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,hjmjohnson/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,hjmjohnson/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,thewtex/ITK,richardbeare/ITK,thewtex/ITK,BRAINSia/ITK,richardbeare/ITK,richardbeare/ITK,thewtex/ITK,BRAINSia/ITK,Kitware/ITK,thewtex/ITK,Kitware/ITK,thewtex/ITK