Finally add kdevelop to the gitignore

[FiniteReality]

Ruby's been telling me to do this for a while, maybe I should actually get around to doing it :)

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Documentation has been added / updated (for bug fixes / features)

What kind of change does this PR introduce? Makes my git status shut up about the .kdev files my IDE creates.

Is there an open issue that this resolves? If so, please link it here. Nope.

What is the current behavior?

$ git status
On branch main
Your branch is ahead of 'origin/main' by 1039 commits.
  (use "git push" to publish your local commits)

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        .kdev4/
        NovelRT.kdev4

nothing added to commit but untracked files present (use "git add" to track)

What is the new behavior (if this is a feature change)?

$ git status
On branch feature/kdevelop-gitignore
Your branch is up to date with 'origin/feature/kdevelop-gitignore'.

nothing to commit, working tree clean

Does this PR introduce a breaking change? If you were expecting to commit editor files that you shouldn't be committing anyway, yes :stuck_out_tongue:

Other information: N/A

[FiniteReality]

In retrospect I should've told CI to skip.