Update dependency petitparser to v7

Author: renovate[bot]

pubspec.yaml

@@ -19,7 +19,7 @@ dependencies:
   analyzer: ^6.4.1
   analyzer_plugin: ^0.11.3
   custom_lint_builder: ^0.6.4
-  petitparser: ^6.0.1
+  petitparser: ^7.0.0
   xml: ^6.3.0
   path: ^1.8.3
   meta: ^1.11.0