`acorn optimize` breaks url inference from filesystem path

[astratagem]

saml-auth/src/AuthServiceProvider.php

Line 74 in babf46d

Url::fromFilesystemPath(dirname($manifestFile))->toString() . '/',

This causes a fatal error when the ViteManifest tries to calculate hash for nonexistent URI.

[astratagem]

FYI @bpizzle since we talked about this error earlier: while there is likely still an upstream bug with cache invalidation, that is not the issue here. It is likely a mistake in the (admittedly hacky) custom function here that tries to put together a URL based on a filesystem path.