Update plausible reporting domain

Since the domain changed, update it for Plausible. Also remove the
unused secret from the GitHub pages config.

.github/workflows/gh-pages.yml

@@ -26,7 +26,6 @@ jobs:
       - name: Build
         env:
           BRIDGETOWN_ENV: production
-          PLAUSIBLE_DOMAIN: ${{ secrets.PLAUSIBLE_DOMAIN }}
         run: bin/bridgetown deploy
 
       - uses: actions/upload-pages-artifact@v1

src/_data/site_metadata.yml

@@ -6,7 +6,7 @@
 
 title: Rails Girls NL
 email: contact@railsgirls.nl
-plausible_domain: "railsgirls.nl"
+plausible_domain: "2023-may.railsgirls.nl"
 description: >-
   Join us for Rails Girls Rotterdam May 2023! A free, one day workshop. Discover the exciting world of web development through Ruby on Rails. With the help and guidance of our coaches, you can create a real web application in a fun and relaxed environment. Are you ready to dive in?
 participant_sign_up_form_url: "https://forms.gle/b924Peh1e84mM7au9"