test(install): the spaced-path --parallel exit was passing for the wrong reason

With a spaced --path, the parallel workers get the path split into words
and reject the stray words as unknown options (the bug #755 fixes). Unknown
options used to exit 0, so every worker "succeeded" having installed
nothing, and this case's exit-code assert passed while the count assert
next to it was already an xfail for #755.

Now that unknown options exit 1, the parent exits non-zero there, which is
the truth. The exit-code assert becomes an xfail for #755 like its
neighbour; both will report "appears to have landed" once #755 merges.

scripts/test-install.sh

@@ -361,7 +361,11 @@ dest="$home/My [Agents]/dest dir"
 list="$home/my agents list.txt"
 { echo "# one agent, listed in a file whose own path has spaces"; echo "$FIRST_ENG_SLUG"; } > "$list"
 run_install "$home" --tool claude-code,codex --parallel --jobs 1 --agents-file "$list" --path "$dest"
-assert_eq 0 "$RUN_STATUS" "--parallel with a spaced/globbed --path exits 0"
+# This used to pass for the wrong reason: the workers get the spaced path split
+# into words, reject the stray words as unknown options, and usage() exited 0,
+# so every worker "succeeded" having installed nothing (the count below).
+# Unknown options exit 1 now, so the exit code tells the truth until #755 lands.
+xfail_eq 0 "$RUN_STATUS" "--parallel with a spaced/globbed --path exits 0" "PR #755"
 xfail_eq 1 "$(count_md "$dest")" \
   "--parallel installs exactly the one selected agent (spaced --path + --agents-file)" "PR #755"