Sync with 2.23.1

* maint-2.23: (44 commits)
  Git 2.23.1
  Git 2.22.2
  Git 2.21.1
  mingw: sh arguments need quoting in more circumstances
  mingw: fix quoting of empty arguments for `sh`
  mingw: use MSYS2 quoting even when spawning shell scripts
  mingw: detect when MSYS2's sh is to be spawned more robustly
  t7415: drop v2.20.x-specific work-around
  Git 2.20.2
  t7415: adjust test for dubiously-nested submodule gitdirs for v2.20.x
  Git 2.19.3
  Git 2.18.2
  Git 2.17.3
  Git 2.16.6
  test-drop-caches: use `has_dos_drive_prefix()`
  Git 2.15.4
  Git 2.14.6
  mingw: handle `subst`-ed "DOS drives"
  mingw: refuse to access paths with trailing spaces or periods
  mingw: refuse to access paths with illegal characters
  ...

unpack-trees.c

@@ -2060,7 +2060,8 @@ static int merged_entry(const struct cache_entry *ce,
 		invalidate_ce_path(old, o);
 	}
 
-	do_add_entry(o, merge, update, CE_STAGEMASK);
+	if (do_add_entry(o, merge, update, CE_STAGEMASK) < 0)
+		return -1;
 	return 1;
 }