Add tests around SDK generation

[blampe]

Our examples currently generate SDKs which don't build. On main for example:

~/src/pulumi-go-provider/examples/credentials main*                                                                                                                                                                                         16:05:27
❯ go build -o pulumi-resource-credentials . && pulumi package gen-sdk ./pulumi-resource-credentials --language dotnet

~/src/pulumi-go-provider/examples/credentials main*                                                                                                                                                                                         16:05:31
❯ cd sdk/dotnet

~/src/pulumi-go-provider/examples/credentials/sdk/dotnet main*                                                                                                                                                                              16:05:34
❯ dotnet build .
Microsoft (R) Build Engine version 17.0.1+b177f8fa7 for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  Restored /Users/bryce/src/pulumi-go-provider/examples/credentials/sdk/dotnet/Pulumi.Credentials.csproj (in 157 ms).
/Users/bryce/src/pulumi-go-provider/examples/credentials/sdk/dotnet/Config/Config.cs(35,127): error CS0019: Operator '??' cannot be applied to operands of type 'HashKind' and 'HashKind' [/Users/bryce/src/pulumi-go-provider/examples/credentials/sdk/dotnet/Pulumi.Credentials.csproj]

Build FAILED.

/Users/bryce/src/pulumi-go-provider/examples/credentials/sdk/dotnet/Config/Config.cs(35,127): error CS0019: Operator '??' cannot be applied to operands of type 'HashKind' and 'HashKind' [/Users/bryce/src/pulumi-go-provider/examples/credentials/sdk/dotnet/Pulumi.Credentials.csproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:01.01

We should have some sanity checks to confirm our examples generate valid SDKs.