Fix Rails/SaveBang offenses in spec/graphql

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/220040.

.rubocop_manual_todo.yml

@@ -159,9 +159,6 @@ Rails/SaveBang:
     - 'spec/factories_spec.rb'
     - 'spec/frontend/fixtures/issues.rb'
     - 'spec/frontend/fixtures/merge_requests.rb'
-    - 'spec/graphql/mutations/merge_requests/set_locked_spec.rb'
-    - 'spec/graphql/mutations/merge_requests/set_wip_spec.rb'
-    - 'spec/graphql/resolvers/boards_resolver_spec.rb'
     - 'spec/lib/after_commit_queue_spec.rb'
     - 'spec/lib/backup/manager_spec.rb'
     - 'spec/lib/gitlab/alerting/alert_spec.rb'

spec/graphql/mutations/merge_requests/set_locked_spec.rb

@@ -41,7 +41,7 @@ RSpec.describe Mutations::MergeRequests::SetLocked do
         let(:locked) { false }
 
         it 'unlocks the discussion' do
-          merge_request.update(discussion_locked: true)
+          merge_request.update!(discussion_locked: true)
 
           expect(mutated_merge_request).not_to be_discussion_locked
         end

spec/graphql/mutations/merge_requests/set_wip_spec.rb

@@ -41,7 +41,7 @@ RSpec.describe Mutations::MergeRequests::SetWip do
         let(:wip) { false }
 
         it 'removes `wip` from the title' do
-          merge_request.update(title: "WIP: working on it")
+          merge_request.update!(title: "WIP: working on it")
 
           expect(mutated_merge_request).not_to be_work_in_progress
         end

spec/graphql/resolvers/boards_resolver_spec.rb

@@ -54,7 +54,7 @@ RSpec.describe Resolvers::BoardsResolver do
       end
 
       it 'returns nil if board not found' do
-        outside_parent = create(board_parent.class.underscore.to_sym)
+        outside_parent = create!(board_parent.class.underscore.to_sym)
         outside_board  = create(:board, name: 'outside board', resource_parent: outside_parent)
 
         expect(resolve_boards(args: { id: global_id_of(outside_board) })).to eq Board.none