ci: Add Go 1.20 and remove Go 1.17

[cleptric]

Adds Go 1.20 to the CI and drops things related to Go 1.17.

[codecov]

Codecov Report

Base: 79.24% // Head: 78.98% // Decreases project coverage by -0.26% ⚠️

Coverage data is based on head (2679077) compared to base (80b98ba).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #563      +/-   ##
==========================================
- Coverage   79.24%   78.98%   -0.26%     
==========================================
  Files          38       38              
  Lines        3859     3859              
==========================================
- Hits         3058     3048      -10     
- Misses        701      709       +8     
- Partials      100      102       +2     

Impacted Files	Coverage Δ
internal/ratelimit/deadline.go	57.14% <0.00%> (-42.86%)	⬇️
integrations.go	89.01% <0.00%> (-2.32%)	⬇️
transport.go	78.37% <0.00%> (-0.85%)	⬇️

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