Add separate setuptools requirements for Python 3.7 and 3.8

68.0.0 is the most recent version of setuptools to support Python 3.7,
and 75.3.2 is the most recent version to support Python 3.8.

Author: jsf9k

pyproject.toml

@@ -13,9 +13,12 @@ requires = [
     # expressions (in compliance with PEP 639):
     # https://setuptools.pypa.io/en/stable/history.html#v77-0-0
     #
-    # Unfortunately setuptools 77.0.0 does not support Python 3.7 and
-    # 3.8.
-    "setuptools>=61.0.0"
+    # setuptools>=68.0.0 was the last version to support Python 3.7.
+    #
+    # setuptools>=75.3.2 was the last version to support Python 3.7.
+    "setuptools>=68.0.0; python_version == '3.7'",
+    "setuptools>=75.3.2; python_version == '3.8'",
+    "setuptools>=77.0.0; python_version >= '3.9'",
 ]
 
 [project]