Allow assertMatchesJsonSnapshot to accept any JSON-serializable value

[LuckyWindsck]

This PR removes the strict type annotation from the $actual parameter in assertMatchesJsonSnapshot() to allow any JSON-serializable value, including JsonSerializable objects.

The underlying JsonDriver already accepts mixed input, so this change relaxes the input constraint to better reflect its capabilities. It also improves consistency with other assertMatches*Snapshot methods, which do not restrict input types.

[LuckyWindsck]

Related commits for parameter types:

1. 04b9f69: $actual -> array|string $actual
2. d1ebc83: array|string $actual -> array|string|null|int|float|bool $actual

Related Issues / PRs:

• Allow arrays to be serialized to json with JsonDriver #58
• allow array serialize #59

[freekmurze]

Thanks!