Support int8 migration versions via new int8-versions feature #498

Job	Run time
Cargo fmt and clippy	15s
set-rust-versions	4s
Build docs	1m 11s
cargo-audit	19s
Test postgres (stable)	1m 52s
Test postgres (nightly)	1m 54s
Test mysql-async (stable)	1m 13s
test-macros-and-cli (stable, windows-latest)	1m 37s
Test postgres (1.75)	1m 43s
Test mysql-async (nightly)	1m 19s
Test mysql (stable)	2m 3s
test-macros-and-cli (stable, ubuntu-latest)	1m 36s
Test mysql-async (1.75)	1m 7s
Test mysql (nightly)	2m 10s
test-macros-and-cli (nightly, windows-latest)	1m 35s
Test Sqlite (stable)	1m 48s
Test mysql (1.75)	2m 10s
test-macros-and-cli (nightly, ubuntu-latest)	1m 32s
Test Sqlite (nightly)	1m 47s
test-macros-and-cli (1.75, windows-latest)	1m 36s
Test tiberius (stable)	1m 51s
Test Sqlite (1.75)	1m 45s
test-macros-and-cli (1.75, ubuntu-latest)	1m 37s
Test tiberius (nightly)	1m 56s
Test tokio-postgres (stable)	57s
Test tiberius (1.75)	1m 53s
Test tokio-postgres (nightly)	57s
Test tokio-postgres (1.75)	1m 0s
CI is green	0s
	40m 47s

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