Update phpstan/phpstan requirement from ^1.12 to ^2.1

[dependabot]

Updates the requirements on phpstan/phpstan to permit the latest version.

Release notes

Sourced from phpstan/phpstan's releases.

2.1.17

Major new features 🚀

• Introducing Editor Mode (phpstan/phpstan-src@74b909a)
  • Learn more: https://phpstan.org/user-guide/editor-mode

Bleeding edge 🔪

• Report new static() in static method of abstract class - level 0 (phpstan/phpstan-src@a5f7c06)

If you want to see the shape of things to come and adopt bleeding edge features early, you can include this config file in your project's phpstan.neon:

includes:
	- vendor/phpstan/phpstan/conf/bleedingEdge.neon

Of course, there are no backwards compatibility guarantees when you include this file. The behaviour and reported errors can change in minor versions with this file included. Learn more

Improvements 🔧

• This release includes improvements and bugfixes from PHPStan 1.12.27

Bugfixes 🐛

• Fix array_column() with explicit null $index_key (#3970), #12945, thanks @​herndlm!
• AlwaysRememberedExpr - use getNativeExprType (phpstan/phpstan-src@222676e)
• Invalidate result cache properly when property hook changes (phpstan/phpstan-src@dff492e, phpstan/phpstan-src@268d7c6)
• Result cache - react to property having abstract/final/asymmetric visibility changed (phpstan/phpstan-src@0ad2a6a)
• Result cache - react to property being virtual changing (phpstan/phpstan-src@e33a560)

Function signature fixes 🤖

• Update libxml_get_errors() (#3973), thanks @​jack-worman!

Internals 🔍

• Call ProcessPromise::cancel() from deferred canceller (phpstan/phpstan-src@df4c1f3)
• Solve some cases of dead code (phpstan/phpstan-src@e1e8302)

... (truncated)

Commits

• 89b5ef6 PHPStan 2.1.17
• ac6dae9 Updated PHPStan to commit ac6dae9b014720d077a4fa371d34ea57e2713cfe
• c4211ad Editor mode docs
• ea816fc Updated PHPStan to commit ea816fcce3d01247137a97423c143b847607b484
• 4c8c60d Update playground-runner
• dd38409 Updated PHPStan to commit dd3840912ea421745a238d139cdd61c87db9106a
• 8d3e66f Updated PHPStan to commit 8d3e66f52b5abf32283b5afa5a75ab3bdd30e6d8
• 08180bd Update errors identifiers
• a8f412a Updated PHPStan to commit a8f412a2ec1bfb455cfc529bb4e8a05a9caf1249
• fed47b1 Updated PHPStan to commit fed47b1c3c57bd319b71d653d17f70973b62e7fc
• Additional commits viewable in compare view

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[dependabot]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.