.github/workflows/build-release.yaml: Fix deadlock on workflow skipping

The recent fix in ba69a12 (.github/workflows: Cancel redundant workflow
runs, 2023-09-08) did not work for the main branch as the error message on
cancelling was [1]:

> Cancelling since a deadlock for concurrency group 'Build Release-refs/heads/main'
> was detected between 'top level workflow' and 'CallPR'

So we now only cancel the CallPR workflow.

[1]: https://github.com/AllenInstitute/MIES/actions/runs/6132292975

.github/workflows/build-release.yml

@@ -8,9 +8,6 @@ on:
 defaults:
   run:
     shell: bash
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
 jobs:
 
   CallPR: