Fix typos in variable and protected method names

[bact]

• variable: packagComparers -> packageComparers
  • This variable is internal, it is safe to be renamed
• protected method: exludeFilesToString -> excludeFilesToString
  • This method is protected, only accessible to within the same package and by subclasses
  • If there is a known subclass of org.spdx.tools.compare.PackageSheet accessing this method, outside of this package, it may not safe to be renamed
  • The file method is available since 23 Sep 2020

[goneall]

protected method: exludeFilesToString -> excludeFilesToString

This should be safe - I don't know of anyone extending the protected compare classes. Since we are introducing a lot of breaking changes with the spec 3 update, this is a good time to make these changes.

[goneall]

LGTM - Thanks @bact