docs: fix the Pkg workspace link in the test README

`pkgdocs.julialang.org/dev/workspaces/` is a 404 -- workspaces have no page
of their own, they are a section of the `Project.toml` reference. Point at
`v1/toml-files/#Workspaces` instead: the anchor resolves to "The
`[workspace]` section", and the versioned channel will not move the way the
`dev` docs did.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: lkdvos

test/README.md

@@ -4,7 +4,7 @@ Tests are driven by [ParallelTestRunner.jl](https://github.com/JuliaTesting/Para
 Every `.jl` file under `test/` is auto-discovered and executed in its own worker process, so test
 files share no state and must be self-contained.
 
-The test environment is a [Pkg workspace](https://pkgdocs.julialang.org/dev/workspaces/) member:
+The test environment is a [Pkg workspace](https://pkgdocs.julialang.org/v1/toml-files/#Workspaces) member:
 `test/Project.toml` declares the test dependencies and resolves the parent package through
 `[sources]`, while the whole workspace shares a single `Manifest.toml` at the repository root.