Speedup building docker images in CI #89

Job	Run time
Build for Linux (linux, amd64)	58s
Build for Linux (linux, amd64)	58s
Build for Windows (windows, amd64)	1m 2s
Build for Windows (windows, amd64)	1m 2s
Linting	1m 37s
Linting	1m 37s
Unit tests	1m 47s
Unit tests	1m 47s
Build for Linux (linux, 386)	1m 2s
Build for Linux (linux, 386)	1m 2s
WASM build test	0s
WASM build test	0s
Initial tests passed	2s
Initial tests passed	2s
Complement (SQLite native)	4m 2s
Complement (SQLite native)	4m 2s
Sytest (SQLite native)	5m 55s
Sytest (SQLite native)	4m 43s
Upgrade tests	7m 18s
Upgrade tests	7m 18s
Integration tests	5m 21s
Integration tests	5m 21s
Complement (SQLite Cgo)	4m 15s
Complement (SQLite Cgo)	4m 15s
Sytest (SQLite Cgo)	6m 51s
Sytest (SQLite Cgo)	6m 51s
Complement (PostgreSQL)	8m 57s
Complement (PostgreSQL)	8m 57s
Sytest (PostgreSQL)	7m 56s
Sytest (PostgreSQL)	7m 56s
Upgrade tests from HEAD-2	7m 21s
Upgrade tests from HEAD-2	7m 21s
Integration tests passed	1s
Integration tests passed	2s
Update Docker images	0s
Update Docker images	0s
	2h 7m 39s

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