Fix MSI test for Windows Canary build

[lrandersson]

Description

This PR updates a test that was failing in the Windows canary build https://github.com/conda/constructor/actions/runs/27581405719/job/81677012823.
The issue was that the test was referencing a file (an image in this case) which isn't available because, Canary builds do:

• First builds a conda package from the source
• Then tests the installed package in an isolated environment (example) D:\a\constructor\constructor\pkgs\constructor_1781618608424\test_tmp\
• Only files listed in recipe/meta.yaml source_files are copied into this test environment
  • This is where it breaks because the file is not part of the environment.

Therefore, dynamically create a temporary image as part of the test and dont reference the example file. Originally when implementing this I only referenced the image because I just needed any image in order to do the test.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[marcoesters]

Only files listed in recipe/meta.yaml source_files are copied into this test environment

Why is this solution preferred over just adding the missing file into source_files?

[lrandersson]

Only files listed in recipe/meta.yaml source_files are copied into this test environment

Why is this solution preferred over just adding the missing file into source_files?

That's a good question and definitely one of the options. I chose this over the other because I didn't want to couple contents of source_files to this specific test. The test doesn't need the example - just any BMP.

Let me know if you've any preference.