Use tox in stubtest CI

Fix reviewdog sed

Add tox install stage

Author: dstansby

.github/workflows/mypy-stubtest.yml

@@ -18,12 +18,6 @@ jobs:
         with:
           python-version: 3.9
 
-      - name: Install mypy
-        run: |
-          pip3 install -r requirements/testing/mypy.txt \
-            -r requirements/testing/all.txt
-          pip3 install .
-
       - name: Set up reviewdog
         run: |
           mkdir -p "$HOME/bin"
@@ -32,13 +26,16 @@ jobs:
               sh -s -- -b "$HOME/bin"
           echo "$HOME/bin" >> $GITHUB_PATH
 
+      - name: Install tox
+        run: python -m pip install tox
+
       - name: Run mypy stubtest
         env:
           REVIEWDOG_GITHUB_API_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           set -o pipefail
-          MPLBACKEND=agg python tools/stubtest.py | \
-              sed -e "s!$pythonLocation/lib/python3.9/site-packages!lib!g" | \
+          tox -e stubtest | \
+              sed -e "s!.tox/stubtest/lib/python3.11/site-packages!lib!g" | \
               reviewdog \
                 -efm '%Eerror: %m' \
                 -efm '%CStub: in file %f:%l' \