Add support for Python 3.10 (#155)

* ni_measurement_generator: Use in-project virtualenvs

* Upgrade pytest to support Python 3.10

* Rerun poetry lock

* PR workflow: Run tests on Python 3.10

* GitHub workflows: Quote version strings to preserve trailing zeroes

* GitHub workflows: Remove unnecessary quotes

* ni-measurement-generator: Don't add test-pypi repo

* Update poetry lock

* GitHub workflow: Try removing grpcio from Poetry cache

* GitHub workflow: Extend previous hack

* Update poetry lock

* PR workflow: Remove Poetry cache debugging hacks

Author: bkeryan

.github/workflows/PR.yml

@@ -70,7 +70,7 @@ jobs:
     strategy:
       matrix:
         os: [macos-latest, windows-latest, ubuntu-latest]
-        python-version: [3.8, 3.9]
+        python-version: [3.8, 3.9, '3.10']
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
@@ -93,4 +93,4 @@ jobs:
         working-directory: ./ni_measurement_generator
       - name: Run tests and Code coverage summary (generator).
         run: poetry run pytest -v
-        working-directory: ./ni_measurement_generator
+        working-directory: ./ni_measurement_generator