Merge commit '5694e24bbf9afccbbf1b44d3a405a4e2bc0ff08d' into glitch-soc/merge-upstream

Conflicts:
- `.github/workflows/build-nightly.yml`:
  Upstream changed the environment variables used for defining the version
  number. This change occurs close to lines that were modified in glitch-soc
  to account for the different repositories to push to.
  Ported upstream changes.
- `.github/workflows/build-push-pr.yml`:
  Upstream changed the environment variables used for defining the version
  number. This change occurs close to lines that were modified in glitch-soc
  to account for the different repositories to push to.
  Ported upstream changes.
- `lib/mastodon/version.rb`:
  Upstream changed how the version string is built from environment variables.
  Adapted the logic to account for the `+glitch` in glitch-soc.

lib/mastodon/version.rb

@@ -16,12 +16,16 @@ module Mastodon
       0
     end
 
-    def flags
-      ENV['MASTODON_VERSION_FLAGS'].presence || '-beta2'
+    def default_prerelease
+      'beta2'
     end
 
-    def suffix
-      "+glitch#{ENV.fetch('MASTODON_VERSION_SUFFIX', '')}"
+    def prerelease
+      ENV['MASTODON_VERSION_PRERELEASE'].presence || default_prerelease
+    end
+
+    def build_metadata
+      ['glitch', ENV.fetch('MASTODON_VERSION_METADATA', nil)].compact.join('.')
     end
 
     def to_a
@@ -29,7 +33,10 @@ module Mastodon
     end
 
     def to_s
-      [to_a.join('.'), flags, suffix].join
+      components = [to_a.join('.')]
+      components << "-#{prerelease}" if prerelease.present?
+      components << "+#{build_metadata}" if build_metadata.present?
+      components.join
     end
 
     def repository