Pin the package_config package used by generate_package_config at version 1.9.3 (#24246) (#24386)

Co-authored-by: Jason Simmons <jason-simmons@users.noreply.github.com>

tools/generate_package_config/pubspec.yaml

diff --git a/tools/generate_package_config/pubspec.yaml b/tools/generate_package_config/pubspec.yaml
index 213dbb9..1afb2e2 100644
--- a/tools/generate_package_config/pubspec.yaml
+++ b/tools/generate_package_config/pubspec.yaml
@@ -5,4 +5,4 @@
 dependencies:
   yaml: any
   pub_semver: any
-  package_config: any
+  package_config: 1.9.3