Updating Playground to GopherJS 1.21.0+go1.21.13 - #83

Updating Playground to GopherJS 1.21.0+go1.21.13#83

grantnelson-wf wants to merge 4 commits into

gopherjs:mastergopherjs/gopherjs.github.io:masterfrom

grantnelson-wf:go1_21_updategrantnelson-wf/gopherjs.github.io:go1_21_updateCopy head branch name to clipboard