DEV: Require uppy.js in theme_qunit_vendor.js (PR #14251)

The smoke test has been failing with the error:

TypeError: Cannot read properties of undefined (reading 'Core')

Since https://github.com/discourse/discourse-encrypt/commit/de20c460770ac37a530518ab3e6d2a5fa2a8627d and 9873a942e3d2df367717f119c591492c690d291d this error has been occurring, possibly now because Uppy is required by a plugin. Adding uppy.js into the require list for theme_qunit_vendor.js fixes the issue.

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