Avoid loading dot files in the mu-plugins directory.

[dcavins]

In some circumstances, metadata files are generated in the mu-plugins directory. For example, editing a plugin file my-mu-plugin.php folder using a Mac via SMB can result in a metadata file ._my-mu-plugin.php being created. Because of the way wp_get_mu_plugins() works, this metadata file will be loaded as a valid plugin and the contents of the file will be output in the page header.

I'm attaching a small patch to avoid loading ._ files in the unfortunate event that they are created.

[dcavins]

Avoid loading ._ files in mu-plugins.

[SergeyBiryukov]

Introduced in [10737].

[azouamauriac]

May be this is related to #41638