🐛 kettle-jem: stop overriding the github git source with SSH in the Gemfile template

gems/kettle-jem/CHANGELOG.md

@@ -39,6 +39,10 @@ Please file a bug if you notice a violation of semantic versioning.
 
 ### Fixed
 
+- The packaged `Gemfile` no longer overrides `git_source(:github)` with an SSH
+  URL. The override was recorded in `Gemfile.lock` as `git@github.com` remotes,
+  which CI runners cannot clone; Bundler's built-in HTTPS source is used again.
+
 - Generated Ruby 4 extracted-stdlib Gemfiles now include `ostruct` so suites
   that require it can run on Rubies where it is no longer bundled by default.
 - Regenerate `sig/*.rbs` signature stubs from the template instead of merging them, preventing a duplicate top-level declaration when the detected namespace kind (module vs. class) changes between runs.

gems/kettle-jem/lib/kettle/jem/templates/Gemfile.example

@@ -8,7 +8,6 @@
 
 source "https://gem.coop"
 
-git_source(:github) { |repo_name| "git@github.com:#{repo_name}.git" }
 git_source(:codeberg) { |repo_name| "https://codeberg.org/#{repo_name}" }
 git_source(:gitlab) { |repo_name| "https://gitlab.com/#{repo_name}" }
 

gems/kettle-jem/spec/integration/structural_merge_template_spec.rb

@@ -2332,9 +2332,10 @@ def gamma
     end
   end
 
-  it "uses SSH for GitHub shorthand dependencies in the packaged Gemfile" do
+  it "uses Bundler's built-in HTTPS source for GitHub shorthand dependencies in the packaged Gemfile" do
     packaged_gemfile = File.read(File.join(described_class::PACKAGED_TEMPLATE_ROOT, "Gemfile.example"))
 
-    expect(packaged_gemfile).to include("git_source(:github) { |repo_name| \"git@github.com:\#{repo_name}.git\" }")
+    # An SSH override is recorded in Gemfile.lock, and CI runners cannot clone SSH remotes.
+    expect(packaged_gemfile).not_to match(/^\s*git_source\(:github\)/)
   end
 end