Fix flaky spec due to retries

What does this MR do and why?

Related to #435355 (closed)

As seen in https://gitlab.com/gitlab-org/gitlab/-/jobs/5754532436, the spec first fails with:

1st Try error in ./spec/requests/api/graphql/boards/board_list_issues_query_spec.rb:117:
[{"message"=>"Timeout on validation of query", "locations"=>[], "extensions"=>{"code"=>"validationTimeout"}}]

And then fails with the wrong issues returned.

This MR aims to fix the 2nd failure. The validation timeout is tracked in #396784.

The failure can be reproduced with:

diff --git a/spec/requests/api/graphql/boards/board_list_issues_query_spec.rb b/spec/requests/api/graphql/boards/board_list_issues_query_spec.rb
index 86e2b2888904..63375a3612a1 100644
--- a/spec/requests/api/graphql/boards/board_list_issues_query_spec.rb
+++ b/spec/requests/api/graphql/boards/board_list_issues_query_spec.rb
@@ -118,6 +118,8 @@ def issue_relative_positions
           issue1.assignee_ids = user.id
           issue2.assignee_ids = another_user.id

+          raise StandardError, "retry me" unless $retried == true
+
           subject

           expect(issue_id).to contain_exactly(issue1.to_gid.to_s, issue2.to_gid.to_s)
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 7317b512ae42..05c7aef0c540 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -85,6 +85,9 @@

   config.verbose_retry = true
   config.display_try_failure_messages = true
+  config.retry_callback = proc do |ex|
+    $retried = true
+  end

   config.infer_spec_type_from_file_location!

And then running:

RSPEC_RETRY_RETRY_COUNT=2 bin/rspec './spec/requests/api/graphql/boards/board_list_issues_query_spec.rb[1:2:1:2:4:1]'

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