Allow Postgres tests to be run on a different database #492

Job	Run time
Build docs	1m 12s
Cargo fmt and clippy	13s
cargo-audit	14s
set-rust-versions	3s
Test Sqlite (stable)	1m 54s
Test Sqlite (nightly)	1m 43s
Test mysql-async (stable)	1m 14s
test-macros-and-cli (stable, windows-latest)	3m 41s
Test mysql (stable)	2m 4s
Test mysql-async (nightly)	1m 15s
Test Sqlite (1.75)	1m 56s
test-macros-and-cli (stable, ubuntu-latest)	2m 0s
Test mysql-async (1.75)	1m 25s
Test mysql (nightly)	2m 8s
test-macros-and-cli (nightly, windows-latest)	4m 36s
Test mysql (1.75)	2m 45s
test-macros-and-cli (nightly, ubuntu-latest)	2m 1s
Test postgres (stable)	2m 14s
test-macros-and-cli (1.75, windows-latest)	4m 35s
Test tiberius (stable)	1m 50s
test-macros-and-cli (1.75, ubuntu-latest)	2m 0s
Test postgres (nightly)	1m 48s
Test tokio-postgres (stable)	52s
Test tiberius (nightly)	1m 51s
Test postgres (1.75)	1m 47s
Test tokio-postgres (nightly)	53s
Test tiberius (1.75)	2m 24s
Test tokio-postgres (1.75)	1m 30s
CI is green	0s
	52m 8s

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