Restore CI operation

Renaming is easier, but GitHub seems to miss CI which is quite a foot/head gun

Author: Byron

.github/workflows/pythonpackage.yml

@@ -5,9 +5,9 @@ name: Python package
 
 on:
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 
 jobs:
   build:
@@ -56,4 +56,4 @@ jobs:
       run: |
         set -x
         pip install -r doc/requirements.txt
-        make -C doc html
+        make -C doc html