Update codecov action to 7.0.0

[srittau]

This should fix CI. The tag is immutable, so should be fine to use: https://github.com/codecov/codecov-action/releases/tag/v7.0.0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.19%. Comparing base (7e4fc36) to head (3003d51).
⚠️ Report is 1 commits behind head on main.

@@           Coverage Diff           @@
##             main     #763   +/-   ##
=======================================
  Coverage   97.19%   97.19%           
=======================================
  Files           3        3           
  Lines        7815     7815           
=======================================
  Hits         7596     7596           
  Misses        219      219           

Flag	Coverage Δ
3.10	88.94% <ø> (ø)
3.10.4	88.94% <ø> (ø)
3.11	88.18% <ø> (ø)
3.11.0	87.43% <ø> (ø)
3.12	88.13% <ø> (ø)
3.12.0	88.12% <ø> (ø)
3.13	82.94% <ø> (ø)
3.13.0	83.65% <ø> (ø)
3.14	79.04% <ø> (ø)
3.9	89.64% <ø> (ø)
3.9.12	89.64% <ø> (ø)
pypy3.10	88.77% <ø> (ø)
pypy3.11	88.04% <ø> (ø)
pypy3.9	89.47% <ø> (ø)

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