[5.0] Fix ProjectResource links hydration

[GrahamCampbell]

Summary

• Fix ProjectResource links hydration when the API returns a decoded JSON object.
• Add regression coverage while preserving existing array input.
• Supersedes Fix error on project resources #348.

Tests

• vendor/bin/phpunit
• vendor/bin/phpstan analyze --no-progress
• docker run -w /data -v "${PWD}":/data:delegated --entrypoint vendor/bin/psalm.phar --rm registry.gitlab.com/grahamcampbell/php:8.1-cli --no-progress
• docker run -w /data -v "${PWD}":/data:delegated --entrypoint vendor/bin/psalm.phar --rm registry.gitlab.com/grahamcampbell/php:8.1-cli --set-baseline=psalm-baseline.xml
• docker run -w /data -v "${PWD}":/data:delegated --entrypoint vendor/bin/phpstan --rm registry.gitlab.com/grahamcampbell/php:8.1-cli analyze --generate-baseline

[GrahamCampbell]

Closing this because it was opened against 5.0 by mistake.