cmd/go/internal/modfetch: fix coderepo test

Fix fixedTagsRepo implements codehost.Repo.
Rename `LatestAt(time.Time, string)` to `Latest()` for fixedTagsRepo.
This change should be include in CL 107657.

Change-Id: I3b51b90c48b49e928562b6f3e83bed61f5664a27
Reviewed-on: https://go-review.googlesource.com/112636
Reviewed-by: Bryan C. Mills <bcmills@google.com>

vendor/cmd/go/internal/modfetch/coderepo_test.go

diff --git a/vendor/cmd/go/internal/modfetch/coderepo_test.go b/vendor/cmd/go/internal/modfetch/coderepo_test.go
index aba2ea3..8821b02 100644
--- a/vendor/cmd/go/internal/modfetch/coderepo_test.go
+++ b/vendor/cmd/go/internal/modfetch/coderepo_test.go
@@ -621,10 +621,10 @@
 	tags []string
 }
 
-func (ch *fixedTagsRepo) Tags(string) ([]string, error)                         { return ch.tags, nil }
-func (ch *fixedTagsRepo) Root() string                                          { return ch.root }
-func (ch *fixedTagsRepo) LatestAt(time.Time, string) (*codehost.RevInfo, error) { panic("not impl") }
-func (ch *fixedTagsRepo) ReadFile(string, string, int64) ([]byte, error)        { panic("not impl") }
+func (ch *fixedTagsRepo) Tags(string) ([]string, error)                  { return ch.tags, nil }
+func (ch *fixedTagsRepo) Root() string                                   { return ch.root }
+func (ch *fixedTagsRepo) Latest() (*codehost.RevInfo, error)             { panic("not impl") }
+func (ch *fixedTagsRepo) ReadFile(string, string, int64) ([]byte, error) { panic("not impl") }
 func (ch *fixedTagsRepo) ReadZip(string, string, int64) (io.ReadCloser, string, error) {
 	panic("not impl")
 }