upgrade.md: Bump minimum Rust version to 1.66.0 (element-hq#17079) (#… #1053

Job	Run time
changes	1s
lint-crlf	4s
check-lockfile	6s
lint-newsfile	0s
check-schema-delta	39s
check-sampleconfig	39s
lint	54s
lint-clippy	26s
Typechecking	1m 28s
lint-clippy-nightly	23s
lint-pydantic	50s
lint-rustfmt	28s
linting-done	3s
calculate-test-jobs	4s
trial-olddeps	6m 54s
portdb (3.8, 11)	3m 1s
complement (monolith, SQLite)	12m 17s
portdb (3.11, 15)	2m 48s
complement (monolith, Postgres)	13m 27s
complement (workers, Postgres)	21m 26s
cargo-bench	0s
cargo-test	0s
trial-pypy	0s
sytest (focal)	8m 9s
trial (3.8, sqlite, all)	4m 12s
sytest (focal, postgres)	10m 9s
trial (3.9, sqlite, all)	4m 1s
sytest (focal, multi-postgres, workers)	13m 39s
trial (3.10, sqlite, all)	3m 53s
sytest (focal, multi-postgres, workers, asyncio)	19m 22s
trial (3.11, sqlite, all)	3m 7s
sytest (focal, asyncio)	9m 59s
trial (3.12, sqlite, all)	3m 43s
sytest (focal, postgres, asyncio)	11m 44s
trial (3.8, postgres, 11, all)	10m 11s
sytest (testing, postgres)	11m 45s
trial (3.12, postgres, 16, all)	9m 31s
trial (3.8, sqlite)	3m 55s
export-data	2m 22s
tests-done	2s
	3h 15m 42s

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