simple-git's custom-binary validation rejects paths containing spaces, so
the default Windows Git install (C:\Program Files\Git\cmd\git.exe) made
every Review pane git call throw and the pane silently showed 'No diffs'.
The binary is resolved inside the Electron main process from known install
locations or PATH — never renderer/user input — so for spaced paths we opt
into simple-git's supported unsafe.allowUnsafeCustomBinary escape hatch
rather than falling back to PATH (often absent in GUI-launched apps).
Simplified from PR #64713 by @unsupportedpastels; supersedes the 8.3
short-path approaches in #55337/#60156.
Fixes#54888