Fix CI: write coverage database to repo root

[nstarman]

Problem

CI was failing on all tests matrix jobs of run 29376673214 even though the test suite itself passed (140 passed). The failure was:

No .coverage file was found in the root directory, this is now a requirement for uploading coverage to Codecov.

The OpenAstronomy tox.yml@v1 reusable workflow now requires a .coverage file in the root of the workspace for every matrix job in order to upload coverage to Codecov (see the OpenAstronomy tox docs).

Root cause

Two things prevented the .coverage file from ending up in the repo root:

1. changedir hides the coverage file. The test environments run in a temporary directory (changedir = .tmp/{envname}), so coverage-enabled envs wrote .coverage there instead of the repo root.
2. Some jobs produced no coverage at all. The py311-test-alldeps jobs (linux/windows/macos) had no cov factor, so they generated no .coverage file and failed the new check regardless of the changedir issue.

Fix

1. Set COVERAGE_FILE = {toxinidir}/.coverage in [testenv] so the coverage database is always written to the repo root, as recommended by the OpenAstronomy docs.
2. Add the -cov factor to the py311-test-alldeps matrix jobs so every matrix job produces a .coverage file.

Verification

• The failing CI run shows the test suite already passing (140 passed); the only failure was the missing .coverage file.
• Confirmed locally that setting COVERAGE_FILE to an absolute path makes pytest-cov write .coverage to that path even when pytest runs from a temporary changedir (and nothing is left behind in the changedir).

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes CI failures in the OpenAstronomy tox.yml@v1 reusable workflow by ensuring every test matrix job produces a .coverage file in the repository root, which is now required for Codecov upload.

Changes:

• Set COVERAGE_FILE = {toxinidir}/.coverage in tox.ini so coverage data is written to the repo root even when changedir is used.
• Update the CI test matrix to run the py311-test-alldeps jobs with the -cov factor across linux/windows/macos so those jobs generate coverage output.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tox.ini	Forces coverage data file location to the repo root to satisfy CI coverage upload requirements despite changedir.
.github/workflows/ci_tests.yml	Adjusts the tox env names so the previously non-coverage py311-test-alldeps jobs run with -cov and generate .coverage.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (6e800fa) to head (24b1300).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #143   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines          320       314    -6     
=========================================
- Hits           320       314    -6     

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