GH Actions: fix build cancelling

Fixes a wrong variable which would cause all builds branched off from the same branch `master` to be cancelled whenever a new branch was pushed, while the build cancelling should only act on a new push for the _actual_ branch pushed.

Author: jrfnl

.github/workflows/cs.yml

@@ -9,7 +9,7 @@ on:
 # Cancels all previous workflow runs for the same branch that have not yet completed.
 concurrency:
   # The concurrency group contains the workflow name and the branch name.
-  group: ${{ github.workflow }}-${{ github.head_ref }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 jobs:

.github/workflows/test.yml

@@ -9,7 +9,7 @@ on:
 # Cancels all previous workflow runs for the same branch that have not yet completed.
 concurrency:
   # The concurrency group contains the workflow name and the branch name.
-  group: ${{ github.workflow }}-${{ github.head_ref }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 jobs: