Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `.github/workflows/build-image.yml`:
  Upstream switched to pushing to both DockerHub and GitHub Container
  Repository, while glitch-soc was already pushing to the latter only.
  Updated our configuration to be slightly more consistent with upstream's
  naming and styling, but kept our behavior.
- `Gemfile.lock`:
  Updated dependencies textually too close to glitch-soc only hcaptcha
  dependency.
  Updated dependencies as upstream did.
- `README.md`:
  Upstream updated its README, but we have a completely different one.
  Kept our README, though it probably should be reworked at some point.
- `app/views/auth/sessions/two_factor.html.haml`:
  Minor style fix upstream that's on a line glitch-soc removed because
  of its different theming system.
  Kept our file as is.
- `spec/controllers/health_controller_spec.rb`:
  This file apparently did not exist upstream, upstream created it with
  different contents but it is functionally the same.
  Switched to upstream's version of the file.
- `spec/presenters/instance_presenter_spec.rb`:
  Upstream changed the specs around `GITHUB_REPOSITORY`, while glitch-soc
  had its own code because it's a fork and does not have the same default
  source URL.
  Took upstream's change, but with glitch-soc's repo as the default case.
- `yarn.lock`:
  Upstream dependencies textually too close to a glitch-soc only one.
  Updated dependencies as upstream did.

spec/presenters/instance_presenter_spec.rb

@@ -89,8 +89,28 @@ describe InstancePresenter do
   end
 
   describe '#source_url' do
-    it 'returns "https://github.com/glitch-soc/mastodon"' do
-      expect(instance_presenter.source_url).to eq('https://github.com/glitch-soc/mastodon')
+    context 'with the GITHUB_REPOSITORY env variable set' do
+      around do |example|
+        ClimateControl.modify GITHUB_REPOSITORY: 'other/repo' do
+          example.run
+        end
+      end
+
+      it 'uses the env variable to build a repo URL' do
+        expect(instance_presenter.source_url).to eq('https://github.com/other/repo')
+      end
+    end
+
+    context 'without the GITHUB_REPOSITORY env variable set' do
+      around do |example|
+        ClimateControl.modify GITHUB_REPOSITORY: nil do
+          example.run
+        end
+      end
+
+      it 'defaults to the core glitch-soc repo URL' do
+        expect(instance_presenter.source_url).to eq('https://github.com/glitch-soc/mastodon')
+      end
     end
   end