[1.x] Fix composer memory limit crashes

[claudiodekker]

This PR fixes an issue where Composer (1.x?) runs out of memory while Jetstream installs stack-dependent packages.
I personally ran into this issue a few weeks ago, but after seeing others on the Inertia.js discord run into it today, I decided to PR it.

Basically, what they'll see is the following:

Fatal error: Allowed memory size of 1610612736 bytes exhausted (tried to allocate 4096 bytes) in phar:///usr/local/Cellar/composer/1.10.8/bin/composer/src/Composer/DependencyResolver/RuleWatchGraph.php on line 52
PHP Fatal error:  Allowed memory size of 1610612736 bytes exhausted (tried to allocate 4096 bytes) in phar:///usr/local/Cellar/composer/1.10.8/bin/composer/src/Composer/DependencyResolver/RuleWatchGraph.php on line 52

By setting the COMPOSER_MEMORY_LIMIT=-1 environment variable, we temporarily unrestrict composer's memory limit to allow for the install to succeed on the first try.