Fixes bug caused by `changes:` array

What does this MR do and why?

Fixes a bug introduced in: !90171 (merged) that caused TypeError: no implicit conversion of Symbol into Integer. The bug occurred when giving an array of filenames to changes without the path keyword, like so :

test1:
  script: exit 0
  rules:
    - changes:
      - README.md

#366923 (closed)

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