cis: switch back to using pyvisa main branch

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install flake8 black isort mypy pytest
-          pip install git+https://github.com/pyvisa/pyvisa.git@vicp
+          pip install git+https://github.com/pyvisa/pyvisa.git@main
       - name: Isort
         run: |
           isort pyvisa_py -c;