Include information about known issues in `Expression.Block` documentation.

### Type of issue

Missing information

### Description

As it was decided to not change current longstanding behavior (https://github.com/dotnet/runtime/issues/128813), pitfalls with current behavior need to be clearly documented.

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.linq.expressions.expression.block?view=net-10.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs-temp/blob/live/xml/System.Linq.Expressions/Expression.xml

### Document Version Independent Id

b653327d-3be2-0266-bd64-82d15d3a10ce

### Platform Id

3a0b8616-00fa-82f9-27ce-60d157fa0e2b

### Article author

@dotnet-bot