`dir` param for key requires trailing slash

[bwitt]

Describe the Bug

When using the key param for a repo, you must have a trailing slash in the dir param or the full path to the key file will be missing a slash between the dir and the key filename.

Expected Behavior

The slash should be added automatically so you do not have to add a trailing slash for dir

Steps to Reproduce

Configure a repo with a key set with dir:

reponame1:
  key:
    name: "filename.asc"
    dir:  "/usr/share/keyrings"
    source: "url1"
  location: "repourl"
  release: "stable"
  repos: "main"

The generated path to the key will be

deb [signed-by=/usr/share/keyringsfilename.asc] repourl stable main

Environment

• Version 10.0.1
• Platform Ubuntu 22.04

Additional Context

Fix is at #1233

[kenyon]

Should have been closed with the merge of #1233.