update codecov action to fix broken gpg key

[petrelharp]

Closes #3465

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.67%. Comparing base (1c689c0) to head (392d190).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3467   +/-   ##
=======================================
  Coverage   91.67%   91.67%           
=======================================
  Files          38       38           
  Lines       32186    32186           
  Branches     5150     5150           
=======================================
  Hits        29505    29505           
  Misses       2348     2348           
  Partials      333      333           

Flag	Coverage Δ
C	82.23% <ø> (ø)
c-python	77.54% <ø> (ø)
python-tests	96.40% <ø> (ø)
python-tests-no-jit	33.20% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Python API	98.70% <ø> (ø)
Python C interface	91.23% <ø> (ø)
C library	91.24% <ø> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[petrelharp]

This worked, so i've tagged v17 in https://github.com/tskit-dev/.github and am bumping things to that one.

[jeromekelleher]

This is great, thanks for fixing. Just fyi, there's no harm in having unaffected things like docs on older tags (but no harm in bumping them either)

[petrelharp]

I've just squashed these; not waiting for checks to pass again.