Google Cloud Storage supports two types of access controls:

1. Uniform bucket level access
1. Fine-grained bucket level access

When Google uniform bucket uniform bucket access is enabled, uploading a
backup via object storage results in the error:

```
Google::Apis::ClientError (invalid: Cannot use ACL API to set object
policy when object policies are disabled.)
```

This happened because previously the backup manager passed in `public:
false`, which would cause fog-google to attempt to set the ACL of the
object to `privateProject`. This must be omitted when uniform
bucket-only policy is used. This is also the default level when
fine-grained bucket level access is used, so specifying the ACL doesn't
add anything.

This mirrors what we did with
https://gitlab.com/gitlab-org/gitlab-foss/merge_requests/26781.

Closes https://gitlab.com/gitlab-org/gitlab/issues/35662