🎨Only use setuptools-scm-git-archive under < py37

`setuptools-scm` support Git archives natively starting v7 but it only
supports Python 3.7 or higher. This patch makes up a set of
conditional build dependencies that add `setuptools-scm-git-archive`
only below Python 3.7 and in combination with an older version of
`setuptools-scm`.

pyproject.toml

@@ -8,8 +8,12 @@ requires = [
   "expandvars",  # needed by in-tree build backend for env vars interpolation
 
   # Plugins
-  "setuptools_scm[toml]>=3.5",
-  "setuptools_scm_git_archive>=1.1",
+  "setuptools-scm >= 7.0.0; python_version >= '3.7'",
+  #  ^    supports git archives through a plugin
+  #  |                                        |
+  # supports git archives natively            V
+  "setuptools-scm[toml] >= 3.5, < 7.0.0; python_version < '3.7'",
+  "setuptools-scm-git-archive >= 1.1; python_version < '3.7'",
 ]
 backend-path = ["packaging"]  # requires 'Pip>=20' or 'pep517>=0.6.0'
 build-backend = "pep517_backend.hooks"