[release/10.0.1xx] [wasm] Always update SDK pack version from workload to current for down level TFM

[github-actions]

Backport of #51269 to release/10.0.1xx

Fixes dotnet/aspnetcore#64049

/cc @maraf

Customer Impact

• Customer reported
• Found internally

dotnet/aspnetcore#64049

Customers building .NET 9 WebAssembly apps using .NET 10 SDK get incorrect build output.

A possible workaround is manually adding an msbuild target to override the computed version right before framework resolution.

Regression

• Yes
• No

Introduced in #50949 which added a fingerprint to the msbuild item identity. The missing update to unified SDK pack version wasn't visible until mentioned change, which was the only one backward incompatible in .NET 10 timeframe. The fact down level targeting was using incorrect version was overseen, because all tests were passing, thanks backward compatibility.

Testing

Manual verification of scenarios, both CLI based and VS based

• SDK without workload installed
• SDK with workload installed
• Building and publishing both Blazor Web with WebAssembly and Blazor WebAssembly standalone apps
• Building and publishing with AOT compilation
• Targeting current (.NET 10) and downlevel (.NET 8 and 9)

Risk

Mid. The area in which the change is contained can be affected by many parameters.