Fix base linter loading warnings

What does this MR do?

Fixes the condition for these warnings showing when loading rails(in dev?)

15:17 $ be rails c
--------------------------------------------------------------------------------
 Ruby:         ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-darwin19]
 GitLab:       13.8.0-pre (f589d1a8336) EE
 GitLab Shell: 13.15.0
 PostgreSQL:   11.9
--------------------------------------------------------------------------------
/Users/dstull/projects/gdk/gitlab/lib/gitlab/danger/base_linter.rb:6: warning: already initialized constant Gitlab::Danger::BaseLinter::MIN_SUBJECT_WORDS_COUNT
/Users/dstull/projects/gdk/gitlab/lib/gitlab/danger/base_linter.rb:6: warning: previous definition of MIN_SUBJECT_WORDS_COUNT was here
/Users/dstull/projects/gdk/gitlab/lib/gitlab/danger/base_linter.rb:7: warning: already initialized constant Gitlab::Danger::BaseLinter::MAX_LINE_LENGTH
/Users/dstull/projects/gdk/gitlab/lib/gitlab/danger/base_linter.rb:7: warning: previous definition of MAX_LINE_LENGTH was here
/Users/dstull/projects/gdk/gitlab/lib/gitlab/danger/base_linter.rb:8: warning: already initialized constant Gitlab::Danger::BaseLinter::WIP_PREFIX
/Users/dstull/projects/gdk/gitlab/lib/gitlab/danger/base_linter.rb:8: warning: previous definition of WIP_PREFIX was here

I introduced the base_linter.rb recently and this popped up with that addition.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team