Fix file type regex on GraphQL asset mutations

Following on from #7327, I modified the regex and ran some tests, and it seems to all be working correctly now.

src/gql/resolvers/mutations/Asset.php

@@ -177,7 +177,7 @@ protected function handleUpload(AssetElement $asset, array $fileInformation): bo
             $dataString = $fileInformation['fileData'];
             $fileData = null;
 
-            if (preg_match('/^data:((?<type>[a-z0-9]+\/[a-z0-9\+]+);)?base64,(?<data>.+)/i', $dataString, $matches)) {
+            if (preg_match('/^data:((?<type>[a-z0-9]+\/[a-z0-9\+\.\-]+);)?base64,(?<data>.+)/i', $dataString, $matches)) {
                 // Decode the file
                 $fileData = base64_decode($matches['data']);
             }