Formatted composer.json using JQ --indent 4

[ibexa-yuna]

Question	Answer
JIRA issue	n/a
Type	improvement
Target Ibexa version	v4.5+
BC breaks	no

Aligned indent of composer.json to 4 spaces, for consistency's sake with the pre-existing conventions, ease of merge-ups and task automation.

Checklist:

• Provided PR description.
• Tested the solution manually.
• Provided automated test coverage.
• Checked that target branch is set correctly.
• Ran PHP CS Fixer for new PHP code (use $ composer fix-cs).
• Asked for a review.