Fix impl SqlOrd postgres > postgres_backend feature flag. #3060

Job	Run time
Compiletests	1m 15s
Check Minimal supported rust version (1.66.0)	2m 8s
Check rustfmt style && run clippy	7m 57s
Check sqlite bundled + Sqlite with asan	5m 2s
Spell Check with Typos	6s
Check (stable, postgres, ubuntu-latest)	7m 15s
Check (stable, postgres, macos-latest)	11m 28s
Check (stable, postgres, windows-2019)	19m 0s
Check (stable, sqlite, ubuntu-latest)	5m 39s
Check (stable, sqlite, macos-latest)	7m 8s
Check (stable, sqlite, windows-2019)	8m 2s
Check (stable, mysql, ubuntu-latest)	5m 56s
Check (stable, mysql, macos-latest)	17m 8s
Check (stable, mysql, windows-2019)	13m 26s
Check (beta, postgres, ubuntu-latest)	7m 13s
Check (beta, postgres, macos-latest)	18m 1s
Check (beta, postgres, windows-2019)	22m 54s
Check (beta, sqlite, ubuntu-latest)	5m 20s
Check (beta, sqlite, macos-latest)	7m 53s
Check (beta, sqlite, windows-2019)	7m 7s
Check (beta, mysql, ubuntu-latest)	5m 57s
Check (beta, mysql, macos-latest)	15m 57s
Check (beta, mysql, windows-2019)	10m 33s
Check (nightly, postgres, ubuntu-latest)	7m 46s
Check (nightly, postgres, macos-latest)	13m 21s
Check (nightly, postgres, windows-2019)	19m 16s
Check (nightly, sqlite, ubuntu-latest)	5m 51s
Check (nightly, sqlite, macos-latest)	9m 5s
Check (nightly, sqlite, windows-2019)	8m 12s
Check (nightly, mysql, ubuntu-latest)	6m 21s
Check (nightly, mysql, macos-latest)	15m 7s
Check (nightly, mysql, windows-2019)	12m 5s
	5h 9m 29s

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