FIX Undefined Exception on makeDir method

[ssmarco]

This is a small fix that was caught by my editor's Intelephense package. Error is undefined type Silverstripe/GridfieldQueuedExport/Jobs/Exception

Description

Manual testing steps

Issues

Pull request checklist

• The target branch is correct
  • See picking the right version
• All commits are relevant to the purpose of the PR (e.g. no debug statements, unrelated refactoring, or arbitrary linting)
  • Small amounts of additional linting are usually okay, but if it makes it hard to concentrate on the relevant changes, ask for the unrelated changes to be reverted, and submitted as a separate PR.
• The commit messages follow our commit message guidelines
• The PR follows our contribution guidelines
• Code changes follow our coding conventions
• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green

[GuySartorelli]

Hiya,

Thank you for this.
Since this is such a small change I'll let you off the hook this time - but in the future please fill out all of the information in the PR description template, check all of the boxes that apply, and create an issue for your PR. This is all outlined in the contribution documentation and there are relevant links right there in the template for your reference.

[GuySartorelli]

Will merge when CI goes green.