test(compat): make the space-in-path premise able to fail (unblocks main)

[fujibee]

main is red on a required check right now, so this blocks landing for every branch.

check-enforced-assertions: 639 unenforceable assertions, baseline is 638.

Where the extra one came from

Bisected across the commits since v1.2.1, running the checker at each:

v1.2.1    638     67a1252   638     626a625   638
df4c597   638     fa826b7   639  <- here      2910722   639

fa826b7 (#771) added tests/test_compat_posix.bats, and with it:

  # The real ps hands us a path with a space -- the premise of the stub above.
  [[ "$raw" == *"Application Support"* ]]

Why the ratchet is right and the baseline should not move

A non-last [[ ]] cannot fail a test on bash 3.2 (#670). This one is the case's
premise — it exists to establish that the real ps on this platform hands
back a path containing a space, which is the whole situation the assertions below
it are about.

Because it cannot fail, it passes for any raw whatsoever. On a platform whose
ps returned something else entirely, the case would sail past its own premise
and then assert against a value that never had the shape in question. The case
statement above it already skips the platforms where the path is unreachable, so
the surviving failure mode is the quiet one: a premise that reads as checked and
is not.

That is the class the ratchet exists to catch, so the fix is the assertion, not
the number.

The change

grep -qF, the idiom the other #850-era cases in this tree settled on:

  grep -qF -- 'Application Support' <<<"$raw"

Verified

check-enforced-assertions: 638 unenforceable assertions, at the baseline (638).   exit 0
bats tests/test_compat_posix.bats -> all cases pass

The mutation is the point of the change, so it is worth stating plainly: with the
old line, replacing Application Support with a string the path never contains
leaves the case green. With the new line it goes red.

[fujibee]

Closing as a duplicate of #887, which is the one being landed: it carries CLEARED from two reviewers at the same head, and it prints what ps actually returned when the premise does not hold — which is the reason the premise exists at all. The comment wording here is being taken across.