Stop shutdown handler outputting in child processes

[kynx]

This fixes #6410

[sebastianbergmann]

@staabm Can you have a look at this? Thanks!

[sebastianbergmann]

composer.lock needs to be updated after composer.json is changed. This is the reason why the CI pipeline failed.

[kynx]

I've removed it as suggested in #6411 (comment)

[staabm]

lgtm - thanks

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.89%. Comparing base (84b19c6) to head (cbccb67).
⚠️ Report is 48 commits behind head on 12.4.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/Runner/ShutdownHandler.php	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               12.4    #6411   +/-   ##
=========================================
  Coverage     95.89%   95.89%           
- Complexity     7406     7407    +1     
=========================================
  Files           789      789           
  Lines         22600    22601    +1     
=========================================
+ Hits          21673    21674    +1     
  Misses          927      927           

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[sebastianbergmann]

@kynx Thank you for working on this. In the future, please follow the contribution guidelines and configure your real name for your Git commits.

@staabm Thank you for reviewing!