Fix property evaluation as bool.

The validation was using a string but the luci property engine
translates the property to boolean.

Bug: https://github.com/flutter/flutter/issues/81855
Change-Id: Ieb7e82d5e18bccb32f6ae2ad1455f291357c4703
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/31320
Reviewed-by: Keyong Han <keyonghan@google.com>
Reviewed-by: Xilai Zhang <xilaizhang@google.com>
Commit-Queue: Godofredo Contreras <godofredoc@google.com>
diff --git a/recipe_modules/repo_util/api.py b/recipe_modules/repo_util/api.py
index d1d2870..785e272 100644
--- a/recipe_modules/repo_util/api.py
+++ b/recipe_modules/repo_util/api.py
@@ -242,7 +242,7 @@
             ('darwin' if self.m.platform.name == 'mac' else 'win'),
         'REVISION': self.get_commit(checkout_path)
     }
-    if self.m.properties.get('gn_artifacts', '') == 'true':
+    if self.m.properties.get('gn_artifacts', False):
       env['FLUTTER_STORAGE_BASE_URL'] = 'https://storage.googleapis.com/flutter_archives_v2'
     env_prefixes = {'PATH': ['%s' % str(flutter_bin), '%s' % str(dart_bin)]}
     return env, env_prefixes