Golang x/website/cmd/golangorg: TestAll failing as of CL 588977

=== RUN   TestAll
    server_test.go:215: GET https://go.dev/doc/go1.24: found link to https://go.dev/issue/67699, should be /issue/67699
    server_test.go:215: GET https://go.dev/doc/next: found link to https://go.dev/issue/67699, should be /issue/67699
--- FAIL: TestAll (49.77s)

E.g., https://ci.chromium.org/b/8741582152981626753.

CL 588977 (CC @randall77) used an absolute rather than relative link in doc/next/3-tools.md, which unfortunately isn't caught by any test in the main Go repo but only in the x/website one.

It'd be good to copy that test or do something equivalent to avoid further occurrences—filed #68633 for that.

Comment From: gopherbot

Change https://go.dev/cl/600656 mentions this issue: doc/next: use relative link to Go issue

Comment From: gopherbot

Change https://go.dev/cl/600816 mentions this issue: WIP: cmd/relnote: add test to check links for problems