Update requirements to be compatible with Python 3.7

Conditionally set importlib_metadata package version based on Python version to ensure compatibility.

Also, conditionally set tox version to ensure compatibility with importlib package.

Author: GreyNewfie

requirements_dev.txt

@@ -4,11 +4,15 @@ bump2version==0.5.11
 wheel==0.33.6
 watchdog==0.9.0
 flake8==3.7.8
-tox==4.8.0
 coverage==4.5.4
 Sphinx==1.8.5
+
+# Version-specific dependencies
+tox==3.24.0; python_version < '3.8'
+tox==4.8.0; python_version >= '3.8'
+importlib_metadata<5.0.0; python_version < '3.8'
+importlib_metadata==7.2.1; python_version >= '3.8'
 twine==4.0.2
-importlib_metadata==7.2.1  # Pin specific version for twine compatibility https://github.com/astral-sh/rye/issues/1180
 
 pytest==7.4.3
 pytest-runner==5.1