Fix typo in project invitation declined test

app/mailers/emails/members.rb

@@ -59,7 +59,7 @@ module Emails
       @member_source = member_source_class.find(source_id)
       @invite_email = invite_email
-      mail(to: recipient(created_by_id, member_source_type == 'project' ? @member_source.group : @member_source),
+      mail(to: recipient(created_by_id, member_source_type == 'Project' ? @member_source.group : @member_source),
            subject: subject('Invitation declined'))
     end

spec/mailers/notify_spec.rb

@@ -779,7 +779,7 @@ describe Notify do
         invitee
       end
-      subject { described_class.member_invite_declined_email('project', project.id, project_member.invite_email, maintainer.id) }
+      subject { described_class.member_invite_declined_email('Project', project.id, project_member.invite_email, maintainer.id) }
       it_behaves_like 'an email sent from GitLab'
       it_behaves_like 'it should not have Gmail Actions links'