Sliding sync: Fix bg update again (v3) #2943

Job	Run time
lint-newsfile	34s
lint-crlf	3s
changes	2s
check-lockfile	4s
check-sampleconfig	49s
lint	45s
check-schema-delta	40s
Typechecking	1m 31s
lint-pydantic	40s
lint-clippy	0s
lint-clippy-nightly	0s
lint-readme	0s
lint-rustfmt	0s
linting-done	3s
calculate-test-jobs	4s
trial-olddeps	7m 53s
portdb (3.8, 11)	3m 14s
complement (monolith, SQLite)	12m 18s
trial-pypy	0s
portdb (3.11, 15)	3m 2s
complement (monolith, Postgres)	13m 19s
complement (workers, Postgres)	20m 30s
cargo-bench	0s
cargo-test	0s
trial (3.8, sqlite, all)	5m 19s
trial (3.8, postgres, 11, all)	12m 25s
sytest (focal)	8m 40s
trial (3.8, sqlite)	4m 45s
sytest (focal, postgres)	10m 42s
sytest (focal, multi-postgres, workers)	13m 18s
sytest (focal, multi-postgres, workers, asyncio)	18m 53s
export-data	2m 34s
tests-done	3s
	2h 22m 10s

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