chore(qa): clear stale PHPStan baseline entry and PHPUnit deprecations

Two pre-existing findings surfaced during the export-feature test run.
Both are trivial housekeeping, not related to the feature:

- phpstan-baseline.neon: drop the stale ignore for
  RequestInput::wantsJson — the method is now called from the
  helpdesk security-level endpoint and the new export flavor helper,
  so PHPStan no longer matched the pattern and failed with
  `ignore.unmatched` (non-ignorable).

- tests/Service/Auth/SsoUserLinkServiceTest.php: replace the deprecated
  isType('array') / isType('string') assertions with the
  PHPUnit 13-compatible isArray() / isString() equivalents.

Gates after cleanup: PHPUnit 1880 OK (0 deprecations), PHPStan 0 errors.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

phpstan-baseline.neon

@@ -150,12 +150,6 @@ parameters:
 			count: 1
 			path: core/Http/Input/RequestInput.php
 
-		-
-			message: '#^Public method "MintyPHP\\Http\\Input\\RequestInput\:\:wantsJson\(\)" is never used$#'
-			identifier: public.method.unused
-			count: 1
-			path: core/Http/Input/RequestInput.php
-
 		-
 			message: '#^Public method "MintyPHP\\Http\\Input\\RequestInputFactory\:\:create\(\)" is never used$#'
 			identifier: public.method.unused