Suppress unearth's collector warning regarding failed links when working with multiple indexes

Is your feature/enhancement proposal related to a problem? Please describe.

Not a problem but low user experience imho:

When additional (private) indexes are added (default pypi is not overwritten), then commands like pdm outdated or pdm list --resolve (basically every command that iterates the configured indexes and uses unearth's collector) is showing these kind of warnings for the index that does not host the package:

Failed to collect links from http://[private index url]/simple/[package name]/: Client Error(404): Not Found

Depending on the count of default or dev dependencies, those warning are flooding the terminal before the actual command output is provided.

The warning seems to originate from here.

Describe the solution you'd like

Since it is expected that some/all packages are not available on all given indexes, these warnings should be suppressed and maybe only shown if verbosity of the command is increased.