CI: fix the branch (#10)

.github/workflows/test-package.yml

diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
index cdc25d9..270ddbe 100644
--- a/.github/workflows/test-package.yml
+++ b/.github/workflows/test-package.yml
@@ -3,9 +3,9 @@
 on:
   # Run on PRs and pushes to the default branch.
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
   schedule:
     - cron: "0 0 * * 0"