Revise error message

Make the error message more concise and polished.

doc/api/notes.md

@@ -403,7 +403,7 @@ Parameters:
 | `merge_request_iid`     | integer        | yes      | The IID of a project merge request                                                                                           |
 | `body`                  | string         | yes      | The content of a note. Limited to 1,000,000 characters.                                                                      |
 | `created_at`            | string         | no       | Date time string, ISO 8601 formatted. Example: `2016-03-11T03:45:40Z` (requires administrator or project/group owner rights) |
-| `merge_request_diff_sha`| string         | no       | The SHA of the head commit which is used to ensure that the merge request hasn't been updated since the API request was sent. This is required for the /merge quick action |
+| `merge_request_diff_sha`| string         | no       | Required for the `/merge` [quick action](../user/project/quick_actions.md). The SHA of the head commit, which ensures the merge request wasn't updated after the API request was sent. |
 
 ### Modify existing merge request note
 

lib/gitlab/quick_actions/merge_request_actions.rb

@@ -24,7 +24,7 @@ module Gitlab
         end
         execution_message do
           if params[:merge_request_diff_head_sha].blank?
-            _("Merge request diff sha parameter is required for the merge quick action.")
+            _("The `/merge` quick action requires the SHA of the head of the branch.")
           elsif params[:merge_request_diff_head_sha] != quick_action_target.diff_head_sha
             _("Branch has been updated since the merge was requested.")
           elsif preferred_strategy = preferred_auto_merge_strategy(quick_action_target)

locale/gitlab.pot

@@ -23439,9 +23439,6 @@ msgstr ""
 msgid "Merge request dependencies"
 msgstr ""
 
-msgid "Merge request diff sha parameter is required for the merge quick action."
-msgstr ""
-
 msgid "Merge request events"
 msgstr ""
 
@@ -37131,6 +37128,9 @@ msgstr ""
 msgid "The URLs for connecting to Elasticsearch. For clustering, add the URLs separated by commas."
 msgstr ""
 
+msgid "The `/merge` quick action requires the SHA of the head of the branch."
+msgstr ""
+
 msgid "The application will be used where the client secret can be kept confidential. Native mobile apps and Single Page Apps are considered non-confidential."
 msgstr ""
 

spec/services/quick_actions/interpret_service_spec.rb

@@ -800,7 +800,7 @@ RSpec.describe QuickActions::InterpretService do
         let(:project) { repository_project }
         let(:service) { described_class.new(project, developer, {}) }
 
-        it_behaves_like 'failed command', 'Merge request diff sha parameter is required for the merge quick action.' do
+        it_behaves_like 'failed command', 'The `/merge` quick action requires the SHA of the head of the branch.' do
           let(:content) { "/merge" }
           let(:issuable) { merge_request }
         end