Fixes workflow (RascalSoftware#86)

Author: DrPaulSharp

.github/workflows/run_tests.yml

@@ -21,6 +21,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-13]
         version: ["3.9", "3.12"]
+    defaults:
       run:
         shell: bash -l {0}