Fix RSpec/ContextWording cop (#24739)

spec/policies/backup_policy_spec.rb

@@ -8,20 +8,20 @@ RSpec.describe BackupPolicy do
   let(:john)    { Fabricate(:account) }
 
   permissions :create? do
-    context 'not user_signed_in?' do
+    context 'when not user_signed_in?' do
       it 'denies' do
         expect(subject).to_not permit(nil, Backup)
       end
     end
 
-    context 'user_signed_in?' do
-      context 'no backups' do
+    context 'when user_signed_in?' do
+      context 'with no backups' do
         it 'permits' do
           expect(subject).to permit(john, Backup)
         end
       end
 
-      context 'backups are too old' do
+      context 'when backups are too old' do
         it 'permits' do
           travel(-8.days) do
             Fabricate(:backup, user: john.user)
@@ -31,7 +31,7 @@ RSpec.describe BackupPolicy do
         end
       end
 
-      context 'backups are newer' do
+      context 'when backups are newer' do
         it 'denies' do
           travel(-3.days) do
             Fabricate(:backup, user: john.user)