setup: Update the minimum required runtime python3 version

Related to T2367

setup.py

@@ -40,6 +40,7 @@ setup(
     description="Software Heritage storage manager",
     long_description=long_description,
     long_description_content_type="text/markdown",
+    python_requires=">=3.7",
     author="Software Heritage developers",
     author_email="swh-devel@inria.fr",
     url="https://forge.softwareheritage.org/diffusion/DSTO/",

[Phabricator Migration user]

Some references in the commit message have been migrated:

• T2367 is now swh-core#2367 (closed)