Don't error on collision

[stxue1]

Resolves #5137

Changelog Entry

To be copied to the draft changelog by merger:

• Don't error when passing through input as the output

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[adamnovak]

This looks fine, I guess we should expect to be able to overwrite an input with itself...

A workflow that swaps two files and outputs them with each others' names might not work properly when bypassing the file store. But I'm not sure it can reasonably be made to; we have the file store for a reason.