Fix "Drupal" typos in core

I'm going to take this issue. @jungle created it for me to learn!

reassigning to myself

Uploading 1st patch.

Uploading a patch for 9.0.x per @jungle's request

• I confirmed there are no other instances of this with:
• grep -ri "\brupal" *
• I verified that the only changes were correcting this typo and nothing else by using git diff --staged --color-words with the patch applied locally.
• I checked RssResponseRelativeUrlFilterTest to see how this is being used. It's essentially part of a data provider, and we're updating both the expected input and the expected output for two test cases. For one of the test cases, the expected input and output are identical; thus three total lines changed.
• I verified that CSpell still passes with the updated dictionary in 9.1.x:
  

  Checking changed files...
  CSPELL: checking all files
  CSpell: Files checked: 1, Issues found: 0 in 0 files
  CSPELL: passed

Since this is just test data and the spelling error does not impact the overall coverage, this is an allowed change in the current development branch (9.1.x) as well as the production branches (9.0.x and 8.9.x). As @jungle mentioned the backport needs to only change the test data (since the dictionary is not present in those branches). Which we have in #7. :)

Adding issue credit for @jungle for mentoring, and to @jperk224 for creating this patch.

Committed #4 to 9.1.x, then committed #7 to 9.0.x and cherry-picked it to 8.9.x.

Congratulations @jperk224 on your first core contribution!