CI: use macos-13, shell:bash, fail-fast:false

macos-latest (arm64) fails in setup-nu; pin to macos-13
for now. Explicit shell:bash ensures nu is found on PATH.

Author: hyiltiz

.github/workflows/test-auto-venv.yml

@@ -9,8 +9,9 @@ on:
 jobs:
     test-auto-venv:
         strategy:
+            fail-fast: false
             matrix:
-                os: [ubuntu-latest, macos-latest]
+                os: [ubuntu-latest, macos-13]
         runs-on: ${{ matrix.os }}
 
         steps:
@@ -22,5 +23,6 @@ jobs:
                   check-latest: true
 
             - name: Run auto-venv tests
+              shell: bash
               working-directory: modules/virtual_environments/auto-venv
               run: nu test_auto_venv.nu