Log Message:
librsvg: updated to 2.56.0

Version 2.56.0

- Fix crash when XML files get recursively included through
  XInclude.  Thanks to Stefan Schiller for catching this.

- When running the suite of reference tests, you can now use the
  TESTS_OUTPUT_DIR environment variable to specify where results for
  failures get written.  See tests/README.md for details.

- The minimum supported Rust version (MSRV) is 1.64.