Add permission key to CI (dart-lang/test_descriptor#43)

pkgs/test_descriptor/.github/workflows/test-package.yml

diff --git a/pkgs/test_descriptor/.github/workflows/test-package.yml b/pkgs/test_descriptor/.github/workflows/test-package.yml
index 6c7108d..79d8757 100644
--- a/pkgs/test_descriptor/.github/workflows/test-package.yml
+++ b/pkgs/test_descriptor/.github/workflows/test-package.yml
@@ -11,6 +11,7 @@
 
 env:
   PUB_ENVIRONMENT: bot.github
+permissions: read-all
 
 jobs:
   # Check code formatting and static analysis on a single OS (linux)