Revert "increase to 10 chars for good measure"

This reverts commit 941230671c.

app/services/project_identifiers/revert_project_to_classic_service.rb

@@ -64,7 +64,7 @@ module ProjectIdentifiers
     def handle_update_failure(classic_id, error)
       Rails.logger.warn "#{self.class}: Could not set identifier '#{classic_id}' for project #{project.id}; " \
                         "falling back to a randomized suffix. (#{error.message})"
-      project.update!(identifier: "project-#{SecureRandom.alphanumeric(10).downcase}")
+      project.update!(identifier: "project-#{SecureRandom.alphanumeric(5).downcase}")
     end
 
     def identifier_generator

spec/services/project_identifiers/revert_project_to_classic_service_spec.rb

@@ -132,7 +132,7 @@ RSpec.describe ProjectIdentifiers::RevertProjectToClassicService do
 
       it "assigns a project-NNNNN fallback identifier" do
         described_class.new(project).call
-        expect(project.reload.identifier).to match(/\Aproject-[a-z0-9]{10}\z/)
+        expect(project.reload.identifier).to match(/\Aproject-[a-z0-9]{5}\z/)
       end
 
       it "logs a warning containing the project id and the conflicting identifier" do

spec/workers/project_identifiers/revert_instance_to_classic_ids_job_spec.rb

@@ -156,7 +156,7 @@ RSpec.describe ProjectIdentifiers::RevertInstanceToClassicIdsJob do
         end
 
         it "assigns project_conflict a project-NNNNN fallback identifier" do
-          expect(project_conflict.reload.identifier).to match(/\Aproject-[a-z0-9]{10}\z/)
+          expect(project_conflict.reload.identifier).to match(/\Aproject-[a-z0-9]{5}\z/)
         end
       end
     end