Remove hardcoded version of rake from Bundler tests

Let them run against the version resolved by the `test_gems.rb` gemfile.

This should fix ruby-core CI job that was broken by the release of rake
13.3.0.

spec/bundler/commands/check_spec.rb

@@ -57,7 +57,7 @@ RSpec.describe "bundle check" do
 
     bundle :check, raise_on_error: false
     expect(err).to include("The following gems are missing")
-    expect(err).to include(" * rake (13.3.0)")
+    expect(err).to include(" * rake (#{rake_version})")
     expect(err).to include(" * actionpack (2.3.2)")
     expect(err).to include(" * activerecord (2.3.2)")
     expect(err).to include(" * actionmailer (2.3.2)")
@@ -76,7 +76,7 @@ RSpec.describe "bundle check" do
     expect(exitstatus).to be > 0
     expect(err).to include("The following gems are missing")
     expect(err).to include(" * rails (2.3.2)")
-    expect(err).to include(" * rake (13.3.0)")
+    expect(err).to include(" * rake (#{rake_version})")
     expect(err).to include(" * actionpack (2.3.2)")
     expect(err).to include(" * activerecord (2.3.2)")
     expect(err).to include(" * actionmailer (2.3.2)")

spec/bundler/support/builders.rb

@@ -24,10 +24,6 @@ module Spec
       Gem::Platform.new(platform)
     end
 
-    def rake_version
-      "13.3.0"
-    end
-
     def build_repo1
       build_repo gem_repo1 do
         FileUtils.cp rake_path, "#{gem_repo1}/gems/"

spec/bundler/support/path.rb

@@ -284,6 +284,10 @@ module Spec
       Dir["#{base_system_gems}/*/*/**/rake*.gem"].first
     end
 
+    def rake_version
+      File.basename(rake_path).delete_prefix("rake-").delete_suffix(".gem")
+    end
+
     def sinatra_dependency_paths
       deps = %w[
         mustermann