fog-google: Cannot insert legacy ACL

[cwjenkins]

Describe the bug
Paperclip fog implementation sets fog_public to true if fog_public isn't specified (default value).
This causes fog-google to throw an exception when the corresponding bucket is using uniform access controls given predefined_acls (fine grain access control) is set (predefinedAcl=publicRead).
If fog_public were set to false then it also causes the same issue given predefinedAcl is set to private in fog-google.

Workaround: setting fog_public to a lambda that returns nil (seems hacky).

To Reproduce

1. Create a GCS account.
2. Create a bucket with uniform access control.
3. Do not config fog_public
4. Try saving an attachment.

Expected behavior
Not specifying fog_public leaves public nil.

Additional context
Issue on their end.
A PR providing a way to skip predefinedAcl if another gem sets it.