Fix CI test link in README

[fabianfett]

Fix CI test link in README

[codecov-commenter]

Codecov Report

Merging #260 (afb7666) into main (57fda42) will increase coverage by 4.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #260      +/-   ##
==========================================
+ Coverage   39.78%   43.82%   +4.03%     
==========================================
  Files         115      115              
  Lines        9513     9520       +7     
==========================================
+ Hits         3785     4172     +387     
+ Misses       5728     5348     -380     

Flag	Coverage Δ
unittests	43.82% <ø> (+4.03%)	⬆️

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

Impacted Files	Coverage Δ
...ces/PostgresNIO/New/PostgresRow-multi-decode.swift	4.44% <0.00%> (+0.19%)	⬆️
...es/PostgresNIO/Connection/PostgresConnection.swift	17.48% <0.00%> (+0.93%)	⬆️
Sources/PostgresNIO/Data/PostgresRow.swift	50.00% <0.00%> (+1.02%)	⬆️
...rces/PostgresNIO/New/Extensions/Logging+PSQL.swift	19.60% <0.00%> (+1.42%)	⬆️
...s/PostgresNIO/New/Data/Array+PostgresCodable.swift	93.25% <0.00%> (+2.24%)	⬆️
...ostgresNIO/Deprecated/PostgresMessageDecoder.swift	95.45% <0.00%> (+2.27%)	⬆️
...ostgresNIO/New/PostgresBackendMessageDecoder.swift	93.28% <0.00%> (+2.98%)	⬆️
...urces/PostgresNIO/New/Messages/ErrorResponse.swift	32.30% <0.00%> (+3.07%)	⬆️
Sources/PostgresNIO/New/PostgresCell.swift	96.77% <0.00%> (+3.22%)	⬆️
...s/PostgresNIO/New/Data/Float+PostgresCodable.swift	76.66% <0.00%> (+3.33%)	⬆️
... and 20 more

[gwynne]

<a href="https://github.com/vapor/postgres-nio/actions/workflows/main-codecov.yml">
    <img src="https://github.com/vapor/postgres-nio/actions/workflows/main-codecov.yml/badge.svg?branch=main&event=push" alt="Continuous Integration">
</a>

The badge will reflect the status of the most recent code coverage update run made against main, which happens whenever a PR is merged - that's the most accurate representation of "CI status" there is for the current CI setup. (And, of course, I have major plans around improving the CI across the board anyway 🙂)

[gwynne]

(Oh, for reference, since I had to hunt it down again myself just now - to get the badge URL for a workflow, go to the Actions tab, select the workflow on the left, and click the ellipsis "…" button to the right of the search field to get a dropdown with a "Create status badge" option. So easy to find! 🙃)

[gwynne]

I hereby approve all these changes that I made all by myself 🤣

(But even if it was 100% me, I still wouldn't have made them without @fabianfett's suggestions ❤️)