chore: raise phpstan to level 5 and fix type mismatch

- Updated phpstan.neon.dist to level 5
- Fixed type parameter in HasInstanceId::hasInstanceId() method from Plain to UnencryptedToken
- Removed unused Plain token import
- Aligns with lcobucci/jwt library token type hierarchy

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Ninerian

phpstan.neon.dist

@@ -1,5 +1,5 @@
 parameters:
-    level: 4
+    level: 5
     paths:
         - ./src
         - ./test

src/Validation/HasInstanceId.php

@@ -14,7 +14,6 @@
 namespace Staffbase\plugins\sdk\Validation;
 
 use Lcobucci\JWT\Token;
-use Lcobucci\JWT\Token\Plain;
 use Lcobucci\JWT\UnencryptedToken;
 use Lcobucci\JWT\Validation\Constraint;
 use Lcobucci\JWT\Validation\ConstraintViolation;
@@ -36,7 +35,7 @@ public function assert(Token $token): void
         }
     }
 
-    private function hasInstanceId(Plain $token): bool
+    private function hasInstanceId(UnencryptedToken $token): bool
     {
         return (bool) $token->claims()->get(SSODataClaimsInterface::CLAIM_INSTANCE_ID);
     }

test/SSOData/SSODataTest.php

@@ -37,8 +37,7 @@ public function testAccessorsGiveCorrectValues(): void
             $this->assertEquals(
                 $tokenData[$key],
                 $ssoData->$fn(),
-                "called $fn expected " .
-                (is_array($tokenData[$key]) ? print_r($tokenData[$key], true) : (string) $tokenData[$key]),
+                "called $fn expected " . print_r($tokenData[$key], true),
             );
         }
     }

test/SSOTokenTest.php

@@ -161,7 +161,7 @@ public function testConstructorAcceptsLeewayForTokenIssuedInTheFuture()
 
         $sso = new SSOToken($this->publicKey, $token, $leeway);
 
-        // Test passes if no exception is thrown during instantiation
+        $this->assertEquals("testPlugin", $sso->getAudience());
     }
 
     /**