Expand constraint on package_config dependency.

analyzer is not ready yet for null safe package_config.

PiperOrigin-RevId: 355441180
diff --git a/pubspec.yaml b/pubspec.yaml
index a96fbcd..14d4c09 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -24,6 +24,6 @@
   build_test: ^1.1.0
   build_web_compilers: '>=1.0.0 <3.0.0'
   http: ^0.13.0-nullsafety.0
-  package_config: ^2.0.0-nullsafety.0
+  package_config: '>=1.9.3 <3.0.0'
   pedantic: ^1.10.0-nullsafety
   test: ^1.16.0-nullsafety.12