setup: remove upper bound limit on python_requires

Setting upper bound version constraints in libraries is a source of
problems for users of those libraries, see:
https://iscinumpy.dev/post/bound-version-constraints/

The intent of the python-tuf version constraint is to ensure we're
using a version of Python which supports all the features we rely
on, this is a better fit for a lower limit.

Suggested-by: Ofek Lev <ofekmeister@gmail.com>
Signed-off-by: Joshua Lock <jlock@vmware.com>

Author: joshuagl

setup.cfg

@@ -34,7 +34,7 @@ license_files = LICENSE LICENSE-MIT
 
 [options]
 packages = find:
-python_requires = ~=3.7
+python_requires = >=3.7
 install_requires =
   requests>=2.19.1
   securesystemslib>=0.22.0