Requires C++20 in python tests

Author: JohanMabille

test_python/setup.py

@@ -78,8 +78,8 @@ def cpp_flag(compiler):
     """Return the -std=c++17 compiler flag  and errors when the flag is
     no available.
     """
-    if has_flag(compiler, '-std=c++17'):
-        return '-std=c++17'
+    if has_flag(compiler, '-std=c++20'):
+        return '-std=c++20'
     else:
         raise RuntimeError('C++17 support is required by xtensor!')