x/playground: formatting a modern go.mod file fails incorrectly with "invalid go version"

[dmitshur]

Consider a playground snippet that includes a go.mod file as if generated by go mod init play.ground using the latest stable version of Go: https://go.dev/play/p/ZtkN19wIOev.

Pressing the "Format" (not "Run") button fails with an incorrect error message:

go.mod:3: invalid go version '1.22.0': must match format 1.23

I suspect this might be fixed if x/playground is updated to a more recent version of x/mod. It's currently using v0.9.0.

(Most x/ repos get automatic monthly updates of x/ dependencies, but x/playground is currently skipped because of #24823. So fixing that might also indirectly fix this issue.)

Issues #32980 and #32614 are also related.

[gopherbot]

Change https://go.dev/cl/566275 mentions this issue: go.mod: update golang.org/x/mod dependency

[dmitshur]

This was indeed fixed by CL 566275.