SQLx

add cfg attrs in tests that implicitly depended on features #251

Job	Run time
Format	6s
Check (async-std, rustls)	2m 39s
Check (tokio, rustls)	2m 43s
Check (tokio, native-tls)	2m 23s
Unit Test (tokio, rustls)	57s
CLI Binaries (windows-latest)	3m 22s
Check (async-std, native-tls)	2m 38s
CLI Binaries (ubuntu-latest)	35s
SQLite	0s
Postgres with SSL client cert	0s
MariaDB	0s
Postgres	0s
MSSQL	-1s
MySQL	-1s
	15m 21s

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