Change MacOS CI table from x86 support to arm64
It'll still be empty, but at least we're listing an architecture that is
supported.
@@ -126,7 +126,7 @@ Actual testing
| | +-------+---------------+-----------------+
| | | PyPy3 | | |
+-----------+----------+-------+---------------+-----------------+
-| | x86 | CP3.7 | | |
+| | arm64 | CP3.7 | | |
| | +-------+---------------+-----------------+
| | | CP3.8 | | |
| | +-------+---------------+-----------------+
