Modify CI environment setup so that we're always using setup.cfg-spec…

…ified versions.

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
     - uses: actions/setup-python@v4.4.0
       with:
         python-version: ${{ env.python_version }}
-    - run: pip install tox~=4.0
+    - run: pip install -e .[dev]
     - run: tox -e towncrier-check
 
   package:
@@ -54,7 +54,7 @@ jobs:
     - uses: actions/setup-python@v4.4.0
       with:
         python-version: ${{ env.python_version }}
-    - run: pip install tox~=4.0
+    - run: pip install -e .[dev]
     - run: tox -e package
     - uses: actions/upload-artifact@v3
       with:
@@ -93,7 +93,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install --upgrade setuptools
-        pip install setuptools_scm[toml]~=7.0 tox~=4.0 coverage[toml]~=7.0
+        pip install $(ls dist/briefcase-*.whl)[dev,test]
     - name: Test
       run: |
         tox -e py --installpkg dist/*.whl
@@ -125,7 +125,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install --upgrade setuptools
-        pip install coverage[toml]~=7.0
+        pip install $(ls dist/briefcase-*.whl)[test]
     - name: Retrieve coverage data
       uses: actions/download-artifact@v3
       with: