Run composer install on build

[thespad]

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• [ ] I have read the contributing guideline and understand that I have made the correct modifications

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Description:

Fix broken build by installing missing dependencies. Fixes #13

Benefits of this PR and context:

How Has This Been Tested?

Tested locally.

Source / References:

[LinuxServer-CI]

I am a bot, here are the test results for this PR: https://ci-tests.linuxserver.io/lspipepr/chevereto/1.5.1-pkg-73e1215d-pr-14/index.html https://ci-tests.linuxserver.io/lspipepr/chevereto/1.5.1-pkg-73e1215d-pr-14/shellcheck-result.xml