add weekly cron env to tox.ini to fix tox 4.9 compatibility

[braingram]

See: https://github.com/spacetelescope/roman_datamodels/pull/261 for more details

tox 4.9 will no longer run environments that are not either:

• prefixed with a python version: e.g. py310 for python 3.10
• listed in tox.ini

This PR adds the weekly cron env test-devdeps-xdist to tox.ini so hopefully it will ~fail in a new way~ succeed next week when run with tox 4.9.

Checklist

• [ ] added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• [ ] updated relevant tests
• [ ] updated relevant documentation
• [ ] updated relevant milestone(s)
• [ ] added relevant label(s)

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (345ae49) 64.01% compared to head (7281f5c) 64.01%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #195 +/- ## ======================================= Coverage 64.01% 64.01% ======================================= Files 101 101 Lines 5558 5558 ======================================= Hits 3558 3558 Misses 2000 2000 ```

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[braingram]

The test failures appear unrelated to the changes in this PR.

Something appears up with test_crds_selectors_vs_datamodel[miri] perhaps a CRDS file was updated?

[braingram]

test_crds_selectors_vs_datamodel[miri] failure (seen in several test runs) is unrelated and due to an update to a file on CRDS.

[zacharyburnett]

LGTM, when tests pass

[braingram]

LGTM, when tests pass

Thanks! All green after rebasing with changes from: https://github.com/spacetelescope/stdatamodels/pull/197