Warn about EOL for py3.7 and below

py3.7 EOL date was 2023-06.

py3.8 EOL date is scheduled for 2024-10, but I think tools will support
it for a while longer, so it's fair not to be too noisy about it
already.

src/cpymad/__init__.py

@@ -21,9 +21,9 @@
 """
 
 
-if sys.version_info < (3, 7):
+if sys.version_info < (3, 8):
     _unsupported_version = (
-        "Support for python 3.6 and below will be removed in a future release!\n"
+        "Support for python 3.7 and below will be removed in a future release!\n"
         "If you need continued support for an older version, let us know at:\n"
         "  https://github.com/hibtc/cpymad/issues")
     warnings.warn(_unsupported_version, DeprecationWarning)