Update tox.ini (#7358)

- Install `requirements_test.txt` into `formatting` & `pylint` environments.
  `import-error` was showing during the `pylint` run for `contributors-txt` & `colorama` in these two environments.
- Bump `minversion` to match the version in `requirements_test.txt`.
- Bump `pre-commit` dependency version in the `mypy` environment to match the version in `requirements_test.txt`.

tox.ini

@@ -1,29 +1,27 @@
 [tox]
-minversion = 2.4
+minversion = 3.0
 envlist = formatting, py37, py38, py39, py310, pypy, benchmark
 skip_missing_interpreters = true
 requires = pip >=21.3.1
 isolated_build = true
 
 [testenv:pylint]
 deps =
-    -r {toxinidir}/requirements_test_min.txt
-    pre-commit~=2.13
+    -r {toxinidir}/requirements_test.txt
 commands =
     pre-commit run pylint --all-files
 
 [testenv:formatting]
 basepython = python3
 deps =
-    -r {toxinidir}/requirements_test_min.txt
-    pre-commit~=2.13
+    -r {toxinidir}/requirements_test.txt
 commands =
     pre-commit run --all-files
 
 [testenv:mypy]
 basepython = python3
 deps =
-    pre-commit~=2.13
+    pre-commit~=2.20
 commands =
     pre-commit run mypy --all-files