Description:
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On PHP 8.1.0, likely following https://wiki.php.net/rfc/restrict_globals_usage, then null coalesce assignment no longer works (when used with a key on $GLOBALS).

Test script:
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<?php

$GLOBALS["x"] = $GLOBALS["x"] ?? [];
var_dump($GLOBALS["x"]); // array(0){}
$GLOBALS["y"] ??= []; // Fatal error: Invalid opcode 23/1/0. in /in/Y4146 on line 5
echo "Done."

Expected result:
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The script outputs the first var_dump (as it does presently) and then echoes Done.

Actual result:
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Fatal error: Invalid opcode 23/1/0. in /in/Y4146 on line 5