chore(ci): run tests against Python 3.9 and 3.10.0-rc.2

Author: mkniewallner

.github/workflows/integration.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8]
+        python-version: ["3.8"]
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/lint.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8]
+        python-version: ["3.8"]
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10.0-rc.2"]
         os: [ubuntu-latest, ubuntu-18.04, macos-latest, windows-latest]
 
     steps:
@@ -48,11 +48,18 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
 
-      - name: Install dependencies
+      - name: Install poetry
         run: |
           python -m pip install --upgrade pip
           python -m pip install --upgrade poetry
-          poetry install
+
+      # New poetry installer doesn't work well with Python 3.10 (see https://github.com/python-poetry/poetry/issues/4210).
+      - name: Use legacy poetry installer
+        if: startsWith(matrix.python-version, '3.10')
+        run: poetry config experimental.new-installer false
+
+      - name: Install dependencies
+        run: poetry install
 
       - name: Test
         shell: bash