Resolve some deprecations and remove igorw/get-in dependency (#1257)

* Remove `igorw/get-in` dependency to simplify code

* Fix phpunit deprecation

* Simplify phpunit's `->will($this->returnValue())` with `->willReturn()`

* Simplify phpunit's `->will($this->returnCallback())` with `->willReturnCallback()`

* Fix deprecated mock builder `setMethds` with `createPartialMock`

* Remove deprecated phpstan `checkGenericClassInNonGenericObjectType` option

* Bump phpunit to 9.6

---------

Co-authored-by: Jonathan Beliën <[email protected]>

Author: norkunas

composer.json

@@ -22,7 +22,7 @@
     },
     "require-dev": {
         "geocoder-php/provider-integration-tests": "^1.6.3",
-        "phpunit/phpunit": "^9.5"
+        "phpunit/phpunit": "^9.6.11"
     },
     "extra": {
         "branch-alias": {