chore(pre-commit): Trim trailing whitespace

[rhysparry]

This pull request includes a small change to the .pre-commit-config.yaml file. The change adds a new hook to fix trailing whitespace.

• .pre-commit-config.yaml: Added trailing-whitespace hook to fix trailing whitespace.

[rhysparry]

This change is part of the following stack:

• chore: Enable pre-commit with end-of-file check #52
  • chore(pre-commit): Trim trailing whitespace #53 ◀
    • chore(pre-commit): Add file integrity checks #54
      • chore(pre-commit): Remove UTF-8 byte order marker #55
        • chore(pre-commit): format C# with CSharpier #56
          • chore(pre-commit): enable commitlint #57
            • chore(pre-commit): enable GitHub action linting #58
              • chore(pre-commit): Configure pre-commit defaults #59

_{Change managed by git-spice.}