Allow enabling ssh server for GitHub Actions CI builds

Allow enabling tmate when launching the workflow manually using
workflow_dispatch trigger.

.github/workflows/ci.yml

@@ -19,6 +19,13 @@ on:
       - .cirrus.yml
       - .github/workflows/codeql.yml
       - appveyor.yml
+  workflow_dispatch:
+    inputs:
+      enable_ssh:
+        type: boolean
+        description: 'Enable ssh server before running the job'
+        required: false
+        default: false
 
 jobs:
   build:
@@ -107,6 +114,7 @@ jobs:
 
       - name: Setup tmate
         uses: mxschmitt/action-tmate@v3
+        if: ${{ github.event_name == 'workflow_dispatch' && inputs.enable_ssh }}
 
       - name: Install dependencies
         run: ./scripts/ci/install.sh