add serde subfeature to tiberius-config #503

Job	Run time
cargo-audit	11s
Cargo fmt and clippy	1m 11s
set-rust-versions	2s
Build docs	43s
Test tokio-postgres (stable)	54s
Test tokio-postgres (nightly)	57s
test-macros-and-cli (stable, windows-latest)	4m 3s
Test tokio-postgres (1.75)	1m 50s
Test postgres (stable)	1m 43s
test-macros-and-cli (stable, ubuntu-latest)	1m 48s
Test Sqlite (stable)	2m 6s
test-macros-and-cli (nightly, windows-latest)	3m 41s
Test postgres (nightly)	1m 44s
Test Sqlite (nightly)	1m 59s
test-macros-and-cli (nightly, ubuntu-latest)	1m 59s
Test postgres (1.75)	2m 8s
Test Sqlite (1.75)	1m 43s
Test mysql (stable)	2m 42s
test-macros-and-cli (1.75, windows-latest)	4m 32s
Test mysql (nightly)	2m 3s
test-macros-and-cli (1.75, ubuntu-latest)	1m 52s
Test mysql (1.75)	2m 27s
Test mysql-async (stable)	1m 4s
Test tiberius (stable)	1m 44s
Test mysql-async (nightly)	1m 29s
Test mysql-async (1.75)	1m 6s
Test tiberius (nightly)	2m 3s
Test tiberius (1.75)	1m 52s
CI is green	1s
	51m 37s

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