Support int8 migration versions via new int8-versions feature #528

Job	Run time
set-rust-versions	8s
cargo-audit	14s
Build docs	52s
Cargo fmt and clippy	1m 20s
Test Sqlite (stable)	1m 48s
Test mysql (stable)	2m 19s
test-macros-and-cli (stable, windows-latest)	3m 43s
Test Sqlite (nightly)	1m 50s
Test postgres (stable)	1m 41s
Test mysql (nightly)	2m 17s
test-macros-and-cli (stable, ubuntu-latest)	2m 24s
Test Sqlite (1.75)	1m 57s
Test postgres (nightly)	1m 46s
Test mysql (1.75)	2m 19s
test-macros-and-cli (nightly, windows-latest)	3m 20s
Test postgres (1.75)	1m 48s
test-macros-and-cli (nightly, ubuntu-latest)	1m 58s
Test mysql-async (stable)	1m 11s
test-macros-and-cli (1.75, windows-latest)	3m 47s
Test tokio-postgres (stable)	1m 25s
Test mysql-async (nightly)	1m 15s
test-macros-and-cli (1.75, ubuntu-latest)	1m 56s
Test tokio-postgres (nightly)	1m 19s
Test tiberius (stable)	1m 55s
Test mysql-async (1.75)	1m 14s
Test tiberius (nightly)	2m 6s
Test tokio-postgres (1.75)	1m 4s
Test tiberius (1.75)	1m 47s
CI is green	0s
	50m 43s

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