ci: run straw build steps with bash (dash has no 'set -o pipefail')

The runner's default shell for run: steps is dash, which errors
'Illegal option -o pipefail' the moment a step runs 'set -euo pipefail'
(the clone step, plus the pre-existing Verify + publish steps). Set
defaults.run.shell: bash for the job; the straw-build image ships bash.

.forgejo/workflows/build.yml

@@ -30,6 +30,12 @@ on:
 jobs:
   build-and-publish:
     runs-on: lucy-rust
+    # Run every step with bash, not the runner's default dash — the steps use
+    # `set -euo pipefail` (pipefail is a bashism; dash errors "Illegal option").
+    # The straw-build image ships /usr/bin/bash.
+    defaults:
+      run:
+        shell: bash
     container:
       image: git.sulkta.com/sulkta-infra/straw-build:latest
     steps: