Control concurrency to only allow one workflow run per PR branch (#708)

Author: ehennestad

.github/workflows/run_tests.yml

@@ -12,6 +12,11 @@ on:
   push:
     branches:
       - main
+
+concurrency:
+  group: ${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   run_tests:
     name: Run MATLAB tests (${{ matrix.matlab-version }})