Software Heritage fallback fixes #3889

Job	Run time
Analyse	3s
Test-macOS (4.14.2)	1s
Build-macOS (4.14.2)	1s
Cygwin	5s
Test-macOS (5.2.0)	1s
Build-Linux (4.08.1)	33s
Build-macOS (5.2.0)	1s
Build-Linux (4.09.1)	34s
Build-Linux (4.10.2)	34s
Hygiene	14s
Build-Linux (4.11.2)	34s
Build-Linux (4.12.1)	35s
Build-Linux (4.13.1)	33s
Build-Linux (5.0.0)	34s
Build-Linux (5.1.1)	34s
Build-Linux (4.14.2)	21s
Build-Linux (5.2.0)	33s
Build-Windows (x86_64-pc-cygwin, x86_64-pc-cygwin, 4.14.2)	8s
Build-Windows (i686-w64-mingw32, x86_64-pc-cygwin, 4.14.2)	9s
Build-Windows (x86_64-w64-mingw32, x86_64-pc-cygwin, 4.14.2)	9s
Build-Windows (i686-pc-windows, x86_64-pc-cygwin, 4.14.2)	8s
Build-Windows (x86_64-pc-windows, x86_64-pc-cygwin, 4.14.2)	9s
Build-Windows (x86_64-w64-mingw32, x86_64-pc-cygwin, 5.2.0)	8s
Upgrade-macOS	1s
Solvers-macOS	1s
Cold-Linux	1s
Doc-Linux	1s
Solvers-Linux	1s
Test-Linux	1s
Upgrade-Linux	1s
	6m 49s

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