Issue #28701: Replace PyUnicode_CompareWithASCIIString with _PyUnicode_EqualToASCIIString.

The latter function is more readable, faster and doesn't raise exceptions.
diff --git a/Python/getargs.c b/Python/getargs.c
index 8aab067..b10e776 100644
--- a/Python/getargs.c
+++ b/Python/getargs.c
@@ -1618,7 +1618,7 @@
                 return cleanreturn(0, &freelist);
             }
             for (i = 0; i < len; i++) {
-                if (!PyUnicode_CompareWithASCIIString(key, kwlist[i])) {
+                if (_PyUnicode_EqualToASCIIString(key, kwlist[i])) {
                     match = 1;
                     break;
                 }