ci: fix rust-src-dir path

Author: mg-twentyone

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

@@ -32,7 +32,7 @@ jobs:
         uses: actions-rust-lang/[email protected]
         with:
           cache: true
-          rust-src-dir: ../bdk-ffi/bdk-ffi
+          rust-src-dir: ${{ github.workspace }}/bdk-ffi/bdk-ffi
 
       - name: "Generate bdk.py"
         env: