chore: go 1.21

[hacdias]

This lets our tests run with Go 1.21 and next (Go 1.22).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 59.89%. Comparing base (b6b7771) to head (384bf56).

@@            Coverage Diff             @@
##             main     #588      +/-   ##
==========================================
- Coverage   65.62%   59.89%   -5.73%     
==========================================
  Files         207      232      +25     
  Lines       25656    28127    +2471     
==========================================
+ Hits        16836    16846      +10     
- Misses       7346     9806    +2460     
- Partials     1474     1475       +1     

see 42 files with indirect coverage changes