fix newly-detected typo in composite types doc #5127

Job	Run time
Check rustfmt style && run clippy	4m 57s
Check (stable, postgres, ubuntu-latest)	7m 49s
Compiletests	1m 42s
Check mysql bundled + Mysql with asan	17m 1s
Check (stable, postgres, macos-13)	12m 10s
Check Minimal supported rust version (1.78.0)	1m 28s
Check (stable, postgres, macos-15)	5m 29s
Check (stable, postgres, windows-2025)	32m 59s
Check postgres bundled + Postgres with asan	9m 45s
Check sqlite bundled + Sqlite with asan	4m 37s
Check sqlite wasm	3m 50s
Check (stable, postgres, ubuntu-22.04-arm)	11m 53s
Check (stable, sqlite, ubuntu-latest)	3m 54s
Check (stable, sqlite, macos-13)	6m 36s
Check (stable, sqlite, macos-15)	1m 52s
Check (stable, sqlite, windows-2025)	6m 22s
Check (stable, sqlite, ubuntu-22.04-arm)	6m 55s
Check (stable, mysql, ubuntu-latest)	8m 4s
Check (stable, mysql, macos-13)	11m 42s
Check (stable, mysql, macos-15)	5m 28s
Check (stable, mysql, windows-2025)	17m 37s
Check (stable, mysql, ubuntu-22.04-arm)	13m 37s
Check (beta, postgres, ubuntu-latest)	7m 59s
Check (beta, sqlite, ubuntu-latest)	3m 56s
Check (beta, mysql, ubuntu-latest)	8m 0s
Check (nightly, postgres, ubuntu-latest)	7m 6s
Check (nightly, sqlite, ubuntu-latest)	3m 35s
Check (nightly, mysql, ubuntu-latest)	7m 42s
	3h 54m 5s

Provide feedback