[macOS] Broken rpaths in individual architecture CI packages

**Describe the bug**
The individual macOS packages from CI have broken QtNetwork rpath'ing

**To Reproduce**
Download a macOS `aarch64` or `x86_64` from CI, install, and execute multipass. The combined package works fine, though.

**Logs**
```
% multipass
dyld[18747]: Library not loaded: @rpath/QtNetwork.framework/Versions/A/QtNetwork
Referenced from: /Library/Application Support/com.canonical.multipass/bin/multipass
Reason: tried: '/Library/Application Support/com.canonical.multipass/lib/QtNetwork.framework/Versions/A/QtNetwork' (code signature invalid in '/Library/Application Support/com.canonical.multipass/lib/QtNetwork.framework/Versions/A/QtNetwork' (errno=1) sliceOffset=0x001B0000, codeBlobOffset=0x00196680, codeBlobSize=0x00007AD0), '/Library/Application Support/com.canonical.multipass/lib/QtNetwork.framework/Versions/A/QtNetwork' (code signature invalid in '/Library/Application Support/com.canonical.multipass/lib/QtNetwork.framework/Versions/A/QtNetwork' (errno=1) sliceOffset=0x001B0000, codeBlobOffset=0x00196680, codeBlobSize=0x00007AD0)
zsh: abort multipass
```

Reproduce the failure with the individual aarch64 and x86_64 macOS CI packages, then inspect the packaging and signing steps that produce the QtNetwork framework and its rpath. Done means both architecture-specific packages launch multipass without the dyld code-signature or rpath error, while the combined package continues to work.

Written by the indexing model from the issue text.