[Pipeline Bug]: Pipelines claim an optional field (PackageFamilyName) is mandatory and not optional.

Based on #404733.

The pipelines throw an error for MSIX installers if `PackageFamilyName` isn't specified. The problem with that is that the error message in the logs say *"Manifest Error: **Optional** field missing."* (Emphasis mine.)

If the field is actually optional, then it should not be (mandatory|a breaker) for the pipelines.

The log: https://dev.azure.com/shine-oss/8b78618a-7973-49d8-9174-4360829d979b/_apis/build/builds/370234/logs/37

### Possible ways to fix it:
A) Change the error message from `Optional field missing.` → `Required field missing.`
B) Change the pipeline so that it no longer treats `PackageFamilyName` as mandatory.

Start with issue #404733 and the linked Azure DevOps pipeline log, focusing on the MSIX manifest validation for PackageFamilyName. Trace where the pipeline decides the field is missing and compare that behavior with the wording in the log. Done means the validation and message consistently reflect whether the field is optional or required.

Written by the indexing model from the issue text.