[24.2] mulled-build-tool fix for packages wo version

[bernt-matthias]

for tools with requirements without version this resulted in a conda install with requirement=None in the package specs which does not work

How to test the changes?

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• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
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  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

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