Fix var_export($domProp, true) after @ silence misbind (#21975)

[PurHur]

Summary

• Root cause: #15916 guard in tryFoldHoistedBoolNullLiteralCallArg rejected folding trailing true whenever producerOrdinal === 0 inside an @ end-block. After @$d->loadHTML(...), var_export($domProp, true) left PropertyFetch mapped to arg1 and arg0 as a stale EXEC_RETURN (true / NULL).
• Fix: reject only when argIndex === 0 (preserve var_export(@get_cfg_var(...), true)).
• Restamp gen-0 lowering_source_fingerprint so north-star5-fast stays green.

Closes #21975

php-src reference

• ext/standard/var.c — PHP_FUNCTION(var_export)
• DOM props: ext/dom/php_dom.c read handlers (repro only)

PHP implementation

• lib/Compiler.php — tryFoldHoistedBoolNullLiteralCallArg error-suppress guard

Test plan

• Issue repro VM + JIT match Zend
• ./script/phpunit.sh --filter 'var_export_dom_prop_return_true|get_cfg_var_display_errors|ErrorSuppressInlineReturnSlot'
• php script/check-bootstrap-gen0-manifest-sync.php → OK
• make north-star5-verify-fast → OK
• ./script/release-readiness.sh --json → "user_release_ready": "yes"

Verification transcript

# repro (VM)
nodeName='p'
data='hello'
onearg='hello'
assign='hello'

# PHPUnit
OK (12 tests, 32 assertions)

check-bootstrap-gen0-manifest-sync: OK (... lowering_source_fingerprint=a3d6cb8b689e…)
north-star5-verify: OK (fast)
"user_release_ready": "yes"

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