fix tox error on python 3.8

Change-Id: I1f2f7789c803024f8feec4d8626564bbec04b386

tox.ini

@@ -1,6 +1,5 @@
 [tox]
 
-
 envlist = py-sqlalchemy
 
 SQLA_REPO = {env:SQLA_REPO:git+https://github.com/sqlalchemy/sqlalchemy.git}
@@ -26,7 +25,7 @@ deps=pytest>4.6,<8.2
      backports.zoneinfo;python_version<"3.9"
      tzdata
      zimports
-     black==24.10.0
+     black==24.10.0;python_version>"3.8"
      greenlet>=1
 
 
@@ -97,7 +96,7 @@ deps=
       pydocstyle<4.0.0
       # used by flake8-rst-docstrings
       pygments
-      black==24.10.0
+      black==24.10.0;python_version>"3.8"
 commands =
      flake8 ./alembic/ ./tests/ setup.py docs/build/conf.py {posargs}
      black --check setup.py tests alembic
@@ -108,5 +107,5 @@ deps=
     sqlalchemy>=2
     mako
     zimports
-    black==24.10.0
+    black==24.10.0;python_version>"3.8"
 commands = python tools/write_pyi.py