[php-src] Issue #10023: Increase Cap on Memory Limit

Issue: https://github.com/php/php-src/issues/10023 Author: oleibman ### Description Our project is growing, and has apparently passed some critical limit. I last ran a successful Phpunit html coverage report about 2 months ago. When I tried to run that report recently, it failed with an out of memory message indicating the memory limit of 2G had been exceeded. I tried running specifying memory_limit=3G. This failed in exactly the same manner, including a message indicating that the memory limit which had been exceeded was still 2G, not 3G. Conceding that there may be things we can do in our project, and that there might be things that Phpunit could be doing differently ... is there a reason for this apparent memory limit cap? Can it be removed or increased (if necessary for 64-bit systems only)?