ci(deps): bump extractions/setup-just from 3 to 4

v4 moves the underlying ``extractions/setup-crate`` pin from v1.4.0
to v2.0.0, which moves the action runtime to Node 24 — supported
natively by GitHub-hosted ``ubuntu-latest``. Both documented inputs
(``just-version`` and ``github-token``) are byte-identical between
v3 and v4; this workflow passes neither, so behavior is unchanged.

Compare: extractions/setup-just@v3...v4
Releases: https://github.com/extractions/setup-just/releases

Author: tony

.github/workflows/docs.yml

@@ -54,7 +54,7 @@ jobs:
 
       - name: Install just
         if: env.PUBLISH == 'true'
-        uses: extractions/setup-just@v3
+        uses: extractions/setup-just@v4
 
       - name: Print python versions
         if: env.PUBLISH == 'true'