make graphql_ws test less timing-sensitive.

[kristjanvalur]

A fix to intermittent test failure in graphql_ws

Description

Due to timing issues on test runners, the exact number of Keepalive messages sent can vary.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[codecov]

Codecov Report

Merging #2785 (61946f7) into main (4519c39) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2785   +/-   ##
=======================================
  Coverage   96.45%   96.45%           
=======================================
  Files         198      198           
  Lines        8244     8244           
  Branches     1500     1500           
=======================================
  Hits         7952     7952           
  Misses        184      184           
  Partials      108      108           

[kristjanvalur]

🎉