GitLab Housekeeper handle more special characters in identifiers

These special characters break the branch name. We might want to use
file paths and namespaced class names in `identifiers` in future and as
such we should strip these out when generating the branch name.

gems/gitlab-housekeeper/lib/gitlab/housekeeper/git.rb

@@ -54,6 +54,7 @@ def create_commit(branch_name, change)
       def branch_name(identifiers)
         # Hyphen-case each identifier then join together with hyphens.
         branch_name = identifiers
+          .map { |i| i.gsub(/[^\w]+/, '-') }
           .map { |i| i.gsub(/[[:upper:]]/) { |w| "-#{w.downcase}" } }
           .join('-')
           .delete_prefix("-")

gems/gitlab-housekeeper/spec/gitlab/housekeeper/git_spec.rb

@@ -9,7 +9,7 @@
   let(:logger) { instance_double(Logger, info: nil) }
   let(:git) { described_class.new(logger: logger) }
   let(:repository_path) { Pathname(Dir.mktmpdir) }
-  let(:test_branch_name) { 'gitlab-housekeeper--test-branch' }
+  let(:test_branch_name) { 'gitlab-housekeeper--some-class--test--branch_123' }
   let(:file_in_master) { 'file_in_master.txt' }
   let(:file_in_another_branch) { 'file_in_another_branch.txt' }
 
@@ -57,7 +57,7 @@ def setup_and_checkout_another_branch
       split over multiple lines!
       COMMIT
 
-      change.identifiers = %w[GitlabHousekeeper TestBranch]
+      change.identifiers = %w[GitlabHousekeeper::SomeClass Test/Branch_123]
 
       Dir.mkdir('files')
       File.write(test_file1, "Content in file 1!")