ci(release): force bash for build-provider-linux container steps

GitHub Actions defaults to `sh -e` for `run:` steps inside a container,
not bash. The Parity CI image's `sh` is dash, which rejects
`set -o pipefail` (and would next break on `${VAR//x/y}` /
`${VAR:0:N}` substitution). Result: the "Stage and archive" step
exited 2 immediately on the dispatch test run.

Pin `defaults.run.shell: bash` at the job level so every `run:` step
in build-provider-linux executes under bash. macOS is unaffected
(non-container, bash is already the default there).

Author: ilchu

.github/workflows/release.yml

@@ -90,6 +90,9 @@ jobs:
       contents: read
     container:
       image: ${{ needs.set-image.outputs.CI_IMAGE }}
+    defaults:
+      run:
+        shell: bash
     steps:
       - name: Checkout
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6