Upload coverage report from main directly (#125)

* Run whole test suite also on pushes to main
* Remove outdated build-docs workflow

.github/workflows/pytest.yaml

@@ -1,6 +1,12 @@
 name: test
 
-on: pull_request
+# TODO workaround for Codecov/squash and merge, a bit wasteful
+# Revise e.g. via https://github.com/codecov/feedback/issues/369
+on: 
+  pull_request:
+  push:
+    branches:
+      - 'main'
 
 jobs:
   test:
@@ -130,7 +136,6 @@ jobs:
         run: |
           source .venv/bin/activate
           pytest --backend ${{ matrix.backend }} --postgres-dsn "postgresql://postgres:postgres@localhost:5432/test" --cov-report xml:.coverage.xml --cov=ixmp4 -rsxX --benchmark-skip --color=yes
-
       #------------------------------
       #  Upload coverage to codecov
       #------------------------------