Update versions and fix branch name in ci.yml

Author: eliben

.github/workflows/ci.yml

@@ -2,10 +2,10 @@ name: pycparser-tests
 on:
   push:
     branches:
-      - master
+      - main
   pull_request:
     branches:
-      - master
+      - main
 
 permissions:
   contents: read
@@ -17,7 +17,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
         os: [ubuntu-latest, macos-latest, windows-latest]
 
     steps: