bug#68811: build hash inconsistency

[Zacchaeus Scheffer]

Some more context might be useful:

Device A (which successfully built qutebrowser over a couple days)
~ $ guix time-machine --commit=deeb7d1f53d7ddfa977b3eadd760312bbd0a2509 -- 
build qutebrowser --dry-run
/gnu/store/i9ir7a26gv1ii98b4bzgvxp1sx0akind-qutebrowser-2.5.4

Device B (trying to avoid building qutebrowser)
~ $ guix time-machine --commit=deeb7d1f53d7ddfa977b3eadd760312bbd0a2509 -- 
build qutebrowser --dry-run
The following derivations would be built:
  /gnu/store/6n9aq7l5x26xfgrbvws7gvscbzvq5gqn-qutebrowser-2.5.4.drv
  /gnu/store/05wj7wf7bdlkm1ar58kpakvp52drrz7p-qtwebengine-5.15.10.drv
  /gnu/store/7nmv55qqw62jwzrd650vm434s3wpi7i3-python-pyqtwebengine-5.15.9.drv

I have noticed in the past that sometimes a package gets built twice
with two hashes, so I went back and checked if device A had built the
6n9..5gqn qutebrowser store item reported by B in addition to the
i9i..ind one A was reporting.  There was no 6n9..5gqn qutebrowser build
on device A.  I don't believe I have never run guix gc on either device.

-Zacchae