Add worflow_dispatch and locks in bundler version

.github/workflows/ci.yml

@@ -6,6 +6,8 @@ on:
     branches:
       - main
       - 'v**'
+  # Allows workflow to be manually run from Actions tab
+  workflow_dispatch:
 
 name: CI
 
@@ -22,7 +24,7 @@ jobs:
       run: |
         docker run --rm \
         --volume="${{ github.workspace }}:/srv/jekyll" \
-        jekyll/jekyll:${{ matrix.jekyll-version }} /bin/bash -c "gem install bundler && chmod -R 777 /srv/jekyll && bundle install && bundle exec jekyll build && bundle exec rake search:init"
+        jekyll/jekyll:${{ matrix.jekyll-version }} /bin/bash -c "gem install bundler -v 2.4.22 && chmod -R 777 /srv/jekyll && bundle install && bundle exec jekyll build && bundle exec rake search:init"
 
   assets:
     name: Test CSS and JS