This pull request updates the handling of `.msix` package extensions in
the software installer logic to clarify support for Fleet-maintained
Windows apps and to ensure custom uploads of `.msix` files remain
unsupported. Test coverage is also expanded to explicitly check these
cases.
**Platform support changes:**
* Updated `packageExtensionToPlatform` in `software_installers.go` to
include `.msix` as a valid extension for Fleet-maintained Windows apps,
while maintaining that custom uploads of `.msix` files are still
rejected.
**Test coverage improvements:**
* Added test cases in `TestSoftwareInstallerPlatformFromExtension` and
`TestSofwareInstallerSourceFromExtensionAndName` to ensure `.msix` files
are correctly handled as unsupported for custom uploads.
[[1]](diffhunk://#diff-581f0146919318ed08c10123ad2f4585bfcfda40cba1dfcb20a65afc40259f32L164-R166)
[[2]](diffhunk://#diff-581f0146919318ed08c10123ad2f4585bfcfda40cba1dfcb20a65afc40259f32L214-R218)
4f9fe1d81b