modules: optional: Update rust for doc fix

Based on review feedback on zephyrproject-rtos#83715, bring in changes to rust documentation
to generate for a vendor neutral platform (qemu).  This also brings in a
small invalid link error that had somehow made it in.

Signed-off-by: David Brown <david.brown@linaro.org>

submanifests/optional.yaml

@@ -60,7 +60,7 @@ manifest:
       groups:
         - optional
     - name: zephyr-lang-rust
-      revision: 7af3db47bf7335ac6a6fe7480df6b41fb46dbe9d
+      revision: cf3dc6cb79631717464f1cd6b3fb122220f12915
       path: modules/lang/rust
       remote: upstream
       groups: