chore: allow phpstan v1

[phil-davis]

"uri" repo is working running phpstan 1.11 on PHP 8.4
So I am hoping that I could find some config that will allow old phpstan 0.12 to keep running with PHP 7.1, and phpstan 1.11 to run with PHP 8.4
But phpstan 1.11 with PHP 8.4 is giving:
"Result is incomplete because of severe errors"
"Some parallel worker jobs have not finished. while running parallel worker"
But the deprecated messages that are logged are similar to what "uri" logs.
There must be difference in something!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.72%. Comparing base (c832947) to head (467bfe3).
Report is 1 commits behind head on 5.1.

Additional details and impacted files

@@            Coverage Diff            @@
##                5.1     #130   +/-   ##
=========================================
  Coverage     99.72%   99.72%           
+ Complexity      118      110    -8     
=========================================
  Files             7        7           
  Lines           365      365           
=========================================
  Hits            364      364           
  Misses            1        1           

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[phil-davis]

Now I am struggling to get PHP 8.4 with phpstan 1.11 to actually report a problem with deprecated stuff.
Maybe the phpstan level has to be higher - in "uri" it is much higher.

[staabm]

for deprecations you need phpstan-deprecation-rules

[phil-davis]

https://github.com/sabre-io/event/actions/runs/10575734407/job/29300024688?pr=130
This correctly reports:

PHP Deprecated:  Sabre\Event\Loop\instance(): Implicitly marking parameter $newLoop as nullable is deprecated, the explicit nullable type must be used instead in /home/runner/work/event/event/lib/Loop/functions.php on line 133

But we have a way to use php-cs-fixer to find these anyway, so I will make a different PR to do that.