Repair 'autobuild' download of 'innosetup' installer

[willend]

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:

The download-URL of innosetup (used to generate the McStas/McXtrace “bulky installers”) has changed. This PR fixes the problem and lets us run the ‘autobuild’ scripts again.

Tested functional on https://github.com/willend/McCode (main)

• Manually triggered run completed OK for McXtrace
• Manually triggered run completed OK for McStas

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Declaration of use of AI-tools

• Please add a checkmark here if you used AI-tools during the work for this contribution
• Furter, please describe how / where and for what the tools were used:

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Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:

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PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution contains something else

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[willend]

I will simply merge as the basictest are not required to complete for this PR. (Manual test completed above.)