Sphinx: corrected target and observed warning

Fictional document handoff. Reading copy; no work is submitted or saved.

Actual Sphinx 8.1.3 generated excerpt. A separate bad build failed on missing-packing.

Document handoff

See Packing before sending the package.

Packing

Retain the source record with the package.

Actual failed-reference message

WARNING: undefined label: 'missing-packing' [ref.ref]
Actual failed-build exit code: 1

The complete native build log remains in the source archive.