Suppression via preprocessor directive is considered unnecessary for some diagnostics

[just-ero]

Full issue information + repro project:
https://github.com/just-ero/roslyn-issues-repros/tree/main/5.0.0/000_CustomDiagnosticSuppression

Version

Roslyn: 5.0.0-1.25204.1 (ad1c386)

Steps to Reproduce

1. Add the following code wherever syntactically applicable:

   #pragma warning disable SYSLIB1054
   
   class C
   {
       [DllImport("_")]
       static extern void M();
   }

2. Target .NET 7.0 or higher.

Expected Behavior

The suppression of SYSLIB1054 is not considered unnecessary.

Actual Behavior

It is.

---

[just-ero]

The problem occurs for other diagnostics as well, for example for the EF* family of diagnostics.

[hamarb123]

I've also seen this issue in VS with other diagnostics (but I hadn't tracked down the specific circumstances to cause it yet, but the one listed here seems about right). This is also a roslyn issue, not a runtime issue.

[just-ero]

Due to apparent confusion on the target repo for this issue, I've attached two screenshots showing both the SYSLIB1054 diagnostic being emitted without the suppression, as well as the suppression being marked as unnecessary when included.