Update GitHub Actions to use 'main' branch

Replaced references to 'master' with 'main' in the `push` and
`pull_request` triggers of the GitHub Actions workflow file
(`tests.yml`). This change aligns the workflow configuration
with the branch renaming for inclusivity and modern conventions.

Author: JunaMeinhold

.github/workflows/tests.yml

@@ -3,10 +3,10 @@ name: Build and Test
 on:
   push:
     branches:
-      - master
+      - main
   pull_request:
     branches:
-      - master
+      - main
 
 jobs:
   build-and-test: