[NOT FOR MERGE] Test enabling Copy-on-Write by default
xref https://github.com/pandas-dev/pandas/issues/48998

We already test with CoW enabled in a few CI builds, but let's see what this gives when enabling it by default for the full test matrix.
This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. I think with https://github.com/pandas-dev/pandas/pull/56633 we have effectively started down this path so closing