Assert fails in NullableWalker with (invalid) statement block in assignment

[jjonescz]

roslyn version 405a8fa

[Fact]
public void Block()
{
    var source = """
        #nullable enable
        string s = {"y"}"x";
        """;
    CreateCompilation(source).VerifyDiagnostics();
}

System.InvalidOperationException : Analyzed 6 nodes in NullableWalker, but DebugVerifier expects 4. Example of unverified node: BoundLiteral "y"
Stack Trace:
src\Compilers\CSharp\Portable\FlowAnalysis\NullableWalker.DebugVerifier.cs(50,0): at Microsoft.CodeAnalysis.CSharp.NullableWalker.DebugVerifier.Verify(ImmutableDictionary`2 analyzedNullabilityMap, SnapshotManager snapshotManagerOpt, BoundNode node)