Stop using the deprecated codecov gem

[elia]

Summary

That gem is deprecated and a migration to the CI integration + copertura is strongly advised.

Ref: https://github.com/solidusio/solidus_stripe/pull/227

Checklist

Check out our PR guidelines for more details.

The following are mandatory for all PRs:

• [ ] I have written a thorough PR description.
• [ ] I have kept my commits small and atomic.
• [ ] I have used clear, explanatory commit messages.

The following are not always needed:

• 📖 I have updated the README to account for my changes.
• 📑 I have documented new code with YARD.
• 🛣️ I have opened a PR to update the guides.
• ✅ I have added automated tests to cover my changes.
• 📸 I have attached screenshots to demo visual changes.

[codecov[bot]]

Codecov Report

Merging #333 (7e72e1a) into main (d8d1752) will increase coverage by 97.05%. The diff coverage is 99.12%.

:exclamation: Current head 7e72e1a differs from pull request most recent head 75fcd69. Consider uploading reports for the commit 75fcd69 to get more accurate results

@@            Coverage Diff             @@
##            main     #333       +/-   ##
==========================================
+ Coverage   0.00%   97.05%   +97.05%     
==========================================
  Files        252      185       -67     
  Lines       5831     4488     -1343     
==========================================
+ Hits           0     4356     +4356     
+ Misses      5831      132     -5699     

Impacted Files	Coverage Δ
.../spec/support/solidus_starter_frontend/capybara.rb	71.42% <75.00%> (ø)
...tes/app/components/product_card_component.html.erb	100.00% <100.00%> (ø)
templates/app/components/product_card_component.rb	100.00% <100.00%> (ø)
...mplates/app/views/products/_products-grid.html.erb	100.00% <100.00%> (+100.00%)	:arrow_up:
templates/spec/components/filter_component_spec.rb	100.00% <100.00%> (ø)
templates/spec/components/image_component_spec.rb	100.00% <100.00%> (ø)
...tes/spec/components/link_to_cart_component_spec.rb	100.00% <100.00%> (ø)
...tes/spec/components/product_card_component_spec.rb	100.00% <100.00%> (ø)
...ates/spec/components/taxons_tree_component_spec.rb	100.00% <100.00%> (ø)
...rollers/checkout_guest_sessions_controller_spec.rb	100.00% <100.00%> (ø)
... and 56 more

... and 259 files with indirect coverage changes

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[elia]

Should we also add a badge?

@kennyadsl done!