ci: enable stricter Bash error checking

Co-authored-by: Matt Sturgeon <matt@sturgeon.me.uk>

.github/workflows/backport.yml

@@ -11,6 +11,10 @@ permissions:
   contents: read
   pull-requests: write
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   backport:
     runs-on: ubuntu-24.04

.github/workflows/check.yml

@@ -11,6 +11,10 @@ on:
 permissions:
   contents: read
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   check:
     name: ${{ matrix.name }}

.github/workflows/conflicts.yml

@@ -7,6 +7,10 @@ on:
       - master
       - release-**
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   conflicts:
     runs-on: ubuntu-24.04

.github/workflows/doc.yml

@@ -10,6 +10,10 @@ concurrency:
   cancel-in-progress: true
   group: pages
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   docs:
     runs-on: ubuntu-24.04

.github/workflows/labels.yml

@@ -17,6 +17,10 @@ permissions:
   contents: read
   pull-requests: write
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   labels:
     name: label-pr

.github/workflows/request-reviewers.yml

@@ -7,6 +7,10 @@ on:
     paths:
       - 'modules/**'
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   request-reviewers:
     runs-on: ubuntu-24.04

.github/workflows/update-flake.yml

@@ -6,6 +6,10 @@ on:
     - cron: "0 0 1 * *"
   workflow_dispatch:
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   flake-update:
     runs-on: ubuntu-24.04