Fixed loading the rules twice

[fatbasstard]

Noticed that Rules are loaded twice when playing around a bit, the _init__ called called twice.

Found that we load the rules from disk twice, since this process loads all Python files from disk dynamically, the Rules actually get initialized twice. Waste of resources and confusion.

I removed this double loading behaviour before, but it looks like to got re-introduced in the following commit: 878f9d7

This PR "restores" this, the Rules are only loaded in in the get_args_filenames if the rules need to be printed.

Some findings:

• If there is a "reason" that the rules should be loaded in the get_args_filenames, that would mean that code technically something is "wrong" (like doing something else than loading the rules)... So "assumed" this changed cannot harm anything (backed by the tests BTW 😛 )
• Recently we added a new method to the rules: initialize(), this is a guaranteed and controlled method from the linter called when processing the rules. Might be an option to enforce using this in rules to as well...

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[codecov]

Codecov Report

Merging #980 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #980      +/-   ##
==========================================
- Coverage   86.85%   86.84%   -0.02%     
==========================================
  Files         133      133              
  Lines        7874     7874              
  Branches     1935     1935              
==========================================
- Hits         6839     6838       -1     
- Misses        638      639       +1     
  Partials      397      397

Impacted Files	Coverage Δ
src/cfnlint/core.py	56.6% <0%> (-0.95%)	⬇️

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