fix: asdf >= v0.16.0 php install

[mkungla]

Description:

From asdf version v0.16.0, this plugin breaks and fails when trying to install a PHP version. This PR introduces a fix that addresses this issue for asdf >= v0.16.0 while ensuring backward compatibility with older versions of asdf. Specifically, the default value of ASDF_CONCURRENCY as 'auto' breaks the PHP compiler.

Additionally, I recommend the maintainers set up the bin/help.deps script in the repository to define platform-specific dependencies, as detailed in the asdf plugin documentation. This will help list and check missing dependencies before attempting to compile new PHP versions.

Years ago, I faced a similar issue while building my own PHP version manager, which you can find here: howiphp. I encountered the same challenge when listing and verifying missing dependencies prior to compiling PHP versions.

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Changes Introduced:

• Fixes compatibility with asdf v0.16.0 and later versions.
• Ensures no breaking changes for versions prior to v0.16.0.

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Testing:

• Tested with asdf v0.16.0 and v0.15.0 to verify proper functionality.
• Maintains compatibility with earlier versions of asdf.