fix: Update Package.swift to use HTTPS for swift-protobuf dependency

[GavinPlusPlus]

Description:

Hey there, this is just a simple change that I made to help fix the setup on my mac for cloning the sample project. Both my friend (@Jack-Severson) and I were having issues with building the demo wallet app in Xcode 15.4 or adding the package to a new project due to an issue with fetching swift-protobuf.

I ultimately narrowed the issue down to the Package.swift file using the SSH format for cloning the swift-protobuf package and timing out on our machines. I changes the the format to HTTPS and was then able to successfully resolve dependencies and build the app.

Checklist:

• My PR follows the contribution guidelines of this project
• My PR is free of third-party dependencies that don't comply with the Allowlist
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked the PR title to follow the conventional commit specification

[goncalo-frade-iohk]

Hey @GavinPlusPlus. Yes sometimes Xcode has problems with ssh. I will merge this today ;)

[goncalo-frade-iohk]

@GavinPlusPlus Im merging without build completed, the build issue is just because of the PR being from a user that doesn't have access to the secrets.
But I tested the PR and it works as expected.