[v2.6.0] Bump from go 1.12 to go 1.17 in go.mod

[fxamacker]

Go 1.12 is obsolete and Go 1.20 is a bit too new. It seems reasonable to specify go 1.17 in go.mod because that is the minimum version that can compile main branch without changes.

A recent PR bumped go.mod to go 1.20 while still allowing Go 1.17 to work. The go.mod can create the impression we don't support Go 1.17-1.19 if a user takes a quick look without reading comments, etc.

It seems reasonable to specify go 1.17 in go.mod:

• it can avoid confusion about what minimum version we actually support
• it passed tests with when compiled with Go 1.17 to 1.21
• it will still use Go 1.18-1.20 features when compiled with Go 1.20+
• it is the first version to support the //go:build syntax and avoiding the old syntax is nice

Please comment here if you have thoughts or concerns about bumping from Go 1.12 to 1.17.

[x448]

@fxamacker most users won't read this issue until after v2.6.0 is released and only if it affects them. You can release v2.6.1 as a fix to support earlier Go version if users open issue to request Go 1.16 or older.

[fxamacker]

Closed by #489

[nickchomey]

1.17 has been out of support for over 2 years now. https://endoflife.date/go

I'm curious why something newer (at this point, 1.23) was not used? Would they require a rewrite?