fleetd #519 review fix: widen two needles to the whole parenthetical

Both arity assertions matched on `jq) returned N field(s)` — a needle
that starts in the middle of the script's `(parser name)` parenthetical.
On a real failure the harness prints `missing <needle>`, so the line
came out as:

  FAIL: empty parser output count: missing jq) returned 0 field(s)

which reads as if the script's own message had an unbalanced paren. It
does not; the needle was just sliced. Matching on
`policy parser (jq) returned N field(s)` makes the failure readable and
also pins that the refusal names the parser it used, which the narrower
needle did not.

make_jq() PATH-prefixes a fake jq, so `_PARSER_NAME` is deterministically
"jq" in both tests; the wider needle cannot flake on a host without jq.

Re-proved on this revision, because a disproof is about a revision and
not a file:

* suite exit 0, "PASS: probe member credentials guards"
* bash -n rc=0 on the test under /bin/bash 3.2.57 and bash 5.3.9
* dropping the empty-parse special case -> FAIL: empty parser output
  count: missing policy parser (jq) returned 0 field(s)
* arity threshold 5 -> 0 -> FAIL: short parser output status
* script restored byte-identical after each, green control after both

scripts/test-probe-member-credentials.sh

@@ -62,14 +62,14 @@ test_short_parser_output_refuses() {
   make_jq "printf '%s\\n' true enforce 3 2"
   run_parser
   assert_equals 5 "$PARSER_RC" "short parser output status"
-  assert_contains 'jq) returned 4 field(s)' "$PARSER_OUTPUT" "short parser output count"
+  assert_contains 'policy parser (jq) returned 4 field(s)' "$PARSER_OUTPUT" "short parser output count"
 }
 
 test_empty_parser_output_reports_zero_fields() {
   make_jq ':'
   run_parser
   assert_equals 5 "$PARSER_RC" "empty parser output status"
-  assert_contains 'jq) returned 0 field(s)' "$PARSER_OUTPUT" "empty parser output count"
+  assert_contains 'policy parser (jq) returned 0 field(s)' "$PARSER_OUTPUT" "empty parser output count"
 }
 
 test_well_formed_policy_prints_name_table() {