Adjust CI config so it runs in all branches

Before this change, CI would only trigger on commits to master branch.
When contributor creates a branch that would later become a PR, they do not want to use master branch.
Instead, they want to use feature-branch.
But before this commit, CI would not run in non-master branch at all, so contributor is unable to test their changes before creating a PR to upstream repository.

Signed-off-by: Marat Radchenko <marat@slonopotamus.org>

.github/workflows/test.yml

@@ -2,7 +2,7 @@ name: CI
 
 on:
   push:
-    branches: [ master ]
+    branches: [ '*' ]
   pull_request:
     branches: [ master ]