This fixes restart after updates not working on Linux.
On Linux we can't reliably get the binary path after an update, because
the original binary was deleted and the path will contain ` (deleted)`.
See: https://github.com/rust-lang/rust/issues/69343
We *could* strip ` (deleted)` off, but that feels nasty. So instead we
save the original binary path, before we do the installation, then
restart.
Later on, we can also change this to be a _new_ binary path returned by
the installers, which we then have to start.
Release Notes:
- N/A
dbebb40956