Restore interp cml

This fixes a current problem with the testing.
For some reason, this CML file got deleted instead of updated in an earlier commit, now on cp/interp_refactor : https://github.com/cpelley/iris/commit/85ea6d53289d28c25d80c70bd52158220c50ffe2

These 2 commits restore the file as it was, then update to fix the test (difference is v. small, apparently due to test now being checksum=False)