chore(deps): switch sitemap_generator to rubygems

Switch from GitHub source to RubyGems for improved stability.

- Remove GitHub lock (was waiting for version > 6.3.0)

- Use RubyGems version 7.0.1 with ~> 7.0 constraint

- sitemap_generator 7.x includes Rails 8 support

The sitemap:refresh rake task works correctly with the new version.

Author: mroderick

Gemfile

@@ -126,4 +126,4 @@ gem 'rollbar'
 gem 'scout_apm'
 
 gem 'carrierwave-aws', '~> 1.6'
-gem 'sitemap_generator', github: 'kjvarga/sitemap_generator', branch: 'master' # LOCKED: When a version higher than 6.3.0 is released, drop this LOCKED.
+gem 'sitemap_generator', '~> 7.0'

Gemfile.lock

@@ -1,11 +1,3 @@
-GIT
-  remote: https://github.com/kjvarga/sitemap_generator.git
-  revision: 747988328566c84b0b8aa1ab898ababc371284dc
-  branch: master
-  specs:
-    sitemap_generator (6.4.0)
-      builder (~> 3.0)
-
 GEM
   remote: https://rubygems.org/
   specs:
@@ -546,6 +538,8 @@ GEM
     simplecov-html (0.12.3)
     simplecov-lcov (0.9.0)
     simplecov_json_formatter (0.1.4)
+    sitemap_generator (7.0.1)
+      builder (~> 3.0)
     slop (3.6.0)
     snaky_hash (2.0.1)
       hashie
@@ -691,7 +685,7 @@ DEPENDENCIES
   simple_form
   simplecov
   simplecov-lcov
-  sitemap_generator!
+  sitemap_generator (~> 7.0)
   sprockets-rails
   stimulus-rails
   stripe