support new ignore directive in go.mod (#2169)

Go 1.25 introduces a new `ignore` directive to specify directories the
go command should ignore.

**What type of PR is this?**

`Feature`

**What package or component does this PR mostly affect?**

`bzlmod/go_mod`

**What does this PR do? Why is it needed?**

This PR ignore the `ignore` directive in go.mod file, to avoid causing
the parsing of the _go.mod_ file to fail when this new Go 1.25 directive
is used.