Fix regression on 'opam upgrade <package>' upgrading unrelated things #4034

Job	Run time
Analyse	3s
Hygiene	24s
Cygwin	6s
Build-macOS (4.14.2)	2m 33s
Build-Linux (4.08.1)	2m 6s
Build-macOS (5.3.0)	3m 7s
Build-Linux (4.09.1)	2m 7s
Test-macOS (4.14.2)	29m 31s
Build-Linux (4.10.2)	2m 10s
Test-macOS (5.3.0)	25m 11s
Build-Linux (4.11.2)	2m 6s
Build-Linux (4.12.1)	2m 9s
Build-Linux (4.13.1)	2m 12s
Build-Linux (5.0.0)	2m 27s
Build-Linux (5.1.1)	2m 13s
Build-Linux (5.2.1)	2m 12s
Build-Linux (4.14.2)	2m 2s
Build-Linux (5.3.0)	2m 7s
Build-Windows (x86_64-pc-cygwin, x86_64-pc-cygwin, 4.14.2)	35m 35s
Build-Windows (i686-w64-mingw32, x86_64-pc-cygwin, 4.14.2)	41m 49s
Build-Windows (x86_64-w64-mingw32, x86_64-pc-cygwin, 4.14.2)	43m 10s
Build-Windows (i686-pc-windows, x86_64-pc-cygwin, 4.14.2)	45m 47s
Build-Windows (x86_64-pc-windows, x86_64-pc-cygwin, 4.14.2)	45m 20s
Build-Windows (x86_64-w64-mingw32, x86_64-pc-cygwin, 5.3.0)	41m 35s
Build-Windows (x86_64-pc-windows, x86_64-pc-cygwin, 5.3.0)	41m 28s
Doc-Linux (4.14.2)	1m 8s
Solvers-Linux (z3, 4.14.2)	54s
Cold-Linux	4m 52s
Doc-Linux (5.3.0)	1m 23s
Test-Linux (4.14.2)	10m 31s
Solvers-Linux (z3, 5.3.0)	52s
Test-Linux (5.3.0)	9m 27s
Solvers-Linux (0install, 4.14.2)	1m 23s
Upgrade-Linux (4.14.2)	1m 20s
Solvers-Linux (0install, 5.3.0)	1m 38s
Upgrade-Linux (5.3.0)	1m 34s
Upgrade-macOS (4.14.2)	1m 53s
Solvers-macOS (z3, 4.14.2)	1m 15s
Upgrade-macOS (5.3.0)	2m 5s
Solvers-macOS (z3, 5.3.0)	1m 23s
Solvers-macOS (0install, 4.14.2)	1m 7s
Solvers-macOS (0install, 5.3.0)	1m 20s
	7h 3m 35s

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