Allow Postgres tests to be run on a different database #494

Job	Run time
cargo-audit	15s
Build docs	1m 12s
Cargo fmt and clippy	1m 37s
set-rust-versions	2s
Test Sqlite (stable)	1m 38s
Test tokio-postgres (stable)	56s
Test mysql (stable)	2m 6s
Test tokio-postgres (nightly)	1m 9s
test-macros-and-cli (stable, windows-latest)	3m 58s
Test tokio-postgres (1.75)	55s
test-macros-and-cli (stable, ubuntu-latest)	1m 59s
Test Sqlite (nightly)	1m 54s
test-macros-and-cli (nightly, windows-latest)	4m 50s
Test mysql (nightly)	2m 20s
Test Sqlite (1.75)	1m 43s
Test mysql (1.75)	2m 5s
test-macros-and-cli (nightly, ubuntu-latest)	2m 4s
Test mysql-async (stable)	1m 9s
test-macros-and-cli (1.75, windows-latest)	4m 57s
Test mysql-async (nightly)	1m 8s
Test postgres (stable)	1m 44s
Test mysql-async (1.75)	1m 9s
Test tiberius (stable)	1m 50s
Test postgres (nightly)	2m 3s
test-macros-and-cli (1.75, ubuntu-latest)	1m 59s
Test tiberius (nightly)	1m 54s
Test postgres (1.75)	1m 50s
Test tiberius (1.75)	1m 55s
CI is green	1s
	52m 22s

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