ci: add rust-src-dir for rust setup (get version from rust toml file)

Author: mg-twentyone

.github/workflows/python-api-docs.yaml

@@ -29,7 +29,10 @@ jobs:
           python-version: "3.12"
 
       - name: "Set up Rust"
-        uses: actions-rust-lang/setup-rust-toolchain@v1
+        uses: actions-rust-lang/[email protected]
+        with:
+          cache: true
+          rust-src-dir: ../bdk-ffi/bdk-ffi
 
       - name: "Generate bdk.py"
         env: