ci: force bash shell for all workflow steps

Self-hosted runner defaults to PowerShell on Windows, causing bash
syntax (if/then/fi, curl line continuations) to fail with parse errors.
Setting defaults.run.shell=bash at workflow level fixes all steps.

.github/workflows/deploy.yml

@@ -20,6 +20,10 @@ concurrency:
   group: deploy-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 
+defaults:
+  run:
+    shell: bash
+
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true