Warn for conditional clauses that are either always true or never true

The below was a typo we overlooked in our repo. Strictly, the expression is "valid" but the possibility it was intended is zero.

Have you considered warning for conditions or clauses in conditions that will either ALWAYS or NEVER be true? In this case, it will always be true. I am guessing such clauses are very rarely intentional.

```xml

```

```
C:\proj\1>dotnet --version
6.0.100-preview.2.21155.3

C:\proj\1>dotnet --info
.NET SDK (reflecting any global.json):
Version: 6.0.100-preview.2.21155.3
Commit: 1a9103db2d

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19042
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\6.0.100-preview.2.21155.3\

Host (useful for support):
Version: 6.0.0-preview.2.21154.6
Commit: 3eaf1f316b

...
```