Better tox configuration (#15777)

It solves two problems:
1. `fix_annotate` and `async_matrix` were removed in
#15728
2. It is better to reuse stuff like `runtests.py` not to rewrite the
same command we already have

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

runtests.py

@@ -48,7 +48,17 @@
 # time to run.
 cmds = {
     # Self type check
-    "self": [executable, "-m", "mypy", "--config-file", "mypy_self_check.ini", "-p", "mypy"],
+    "self": [
+        executable,
+        "-m",
+        "mypy",
+        "--config-file",
+        "mypy_self_check.ini",
+        "-p",
+        "mypy",
+        "-p",
+        "mypyc",
+    ],
     # Lint
     "lint": ["pre-commit", "run", "--all-files"],
     # Fast test cases only (this is the bulk of the test suite)

tox.ini

@@ -53,5 +53,5 @@ passenv =
     MYPY_FORCE_COLOR
     MYPY_FORCE_TERMINAL_WIDTH
 commands =
-    python -m mypy --config-file mypy_self_check.ini -p mypy -p mypyc
-    python -m mypy --config-file mypy_self_check.ini misc --exclude misc/fix_annotate.py --exclude misc/async_matrix.py --exclude misc/sync-typeshed.py
+    python runtests.py self
+    python -m mypy --config-file mypy_self_check.ini misc --exclude misc/sync-typeshed.py