Drop support for Go 1.19

[MrAlias]

• Remove CI workflow for Go 1.19
• Update Makefile compat instruction to use 1.20
• Update README.md
• Update all the go.mod directives to use "go 1.20"

Fix #4298

[codecov]

Codecov Report

Merging #4352 (d9dfdc9) into main (6e91434) will increase coverage by 1.0%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            main   #4352     +/-   ##
=======================================
+ Coverage   82.2%   83.3%   +1.0%     
=======================================
  Files        144     145      +1     
  Lines      10002   10007      +5     
=======================================
+ Hits        8229    8338    +109     
+ Misses      1634    1528    -106     
- Partials     139     141      +2     

see 5 files with indirect coverage changes

[yurishkuro]

@MrAlias is there a script that does this across the board?

[MrAlias]

@MrAlias is there a script that does this across the board?

@yurishkuro:

for f in $( find -type f -name 'go.mod' ); do sed -i 's/^\(go \)1.1[0-9]/\11.20/' $f; done

[yurishkuro]

so no.