Pin French sync to action-translation v0.16.0

This PR predated the v0.16.0 release, so it pinned v0.15.0 (default model
claude-sonnet-4-6). v0.16.0 defaults to claude-sonnet-5, which is the point of
pointing French at it.

Diverges deliberately from the fa and zh-cn sync workflows, which stay on
v0.15.0/Sonnet 4.6: French is the edition evaluated on Sonnet 5, and silently
changing the model for two established editions is not this PR's business.

Author: mmcky

.github/workflows/sync-translations-fr.yml

@@ -24,7 +24,7 @@ jobs:
         with:
           fetch-depth: 2
 
-      - uses: QuantEcon/action-translation@v0.15.0
+      - uses: QuantEcon/action-translation@v0.16.0
         with:
           mode: sync
           target-repo: QuantEcon/lecture-python-programming.fr