refactor: go1.21.0 messup dependency

[echoface]

minor version declaration cause problem when user go mod tidy; it will downgrade or change user's toolchain instruction and mess up dependencies

[echoface]

@spf13 @sagikazarmark please review ，thanks

[sagikazarmark]

I'm not entirely sure why this is necessary.

As of Go 1.21, that's the correct notation: https://go.dev/doc/go1.21#tools

(In fact, as of Go 1.23 it's the only accepted notation)

It declares a minimum required version, so as longs you have something later in your toolchain, it shouldn't cause any issues.

Can you please show me an example where it causes trouble? Thanks!