fix: Fix deprecation notices found from GHA workflow run

See https://github.com/jsonrainbow/json-schema/actions/runs/10216569969/job/28268331091

Author: DannyvdSluijs

src/JsonSchema/Uri/UriRetriever.php

@@ -84,7 +84,7 @@ public function confirmMediaType($uriRetriever, $uri)
         }
 
         foreach ($this->allowedInvalidContentTypeEndpoints as $endpoint) {
-            if (strpos($uri, $endpoint) === 0) {
+            if (!\is_null($uri) && strpos($uri, $endpoint) === 0) {
                 return true;
             }
         }

tests/Uri/UriRetrieverTest.php

@@ -300,7 +300,7 @@ public function testPackageURITranslation()
         $root = sprintf('file://%s/', realpath(__DIR__ . '/../..'));
 
         $uri = $retriever->translate('package://foo/bar.json');
-        $this->assertEquals("${root}foo/bar.json", $uri);
+        $this->assertEquals("{$root}foo/bar.json", $uri);
     }
 
     public function testDefaultDistTranslations()