Remove support for python3.8

The C code generated by cython 3.1 requires python 3.8.

.github/build/linux/cpymad.sh

@@ -23,7 +23,9 @@ export LDFLAGS="-fno-lto"
 python setup.py sdist
 
 for PYBIN in /opt/python/cp3*/bin; do
-    "${PYBIN}/pip" wheel dist/*.tar.gz --no-deps -w rawdist/
+    if "${PYBIN}/python" -c "import sys;exit(sys.version_info<(3,8))"; then
+        "${PYBIN}/pip" wheel dist/*.tar.gz --no-deps -w rawdist/
+    fi
 done
 
 # Bundle external shared libraries into the wheels

src/cpymad/__init__.py

@@ -21,9 +21,9 @@
 """
 
 
-if sys.version_info < (3, 8):
+if sys.version_info < (3, 9):
     _unsupported_version = (
-        "Support for python 3.7 and below will be removed in a future release!\n"
+        "Support for python 3.8 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)