[llvm] [llvm] Migrate away from PointerUnion::{is, get, dyn_cast} (NFC) (PR #115626)

[Thorsten Schütt via llvm-commits]

================
@@ -1052,9 +1052,9 @@ class AssignmentTrackingLowering {
       if (Source.isNull())
         OS << "null";
       else if (isa<DbgAssignIntrinsic *>(Source))
----------------
tschuett wrote:

shouldn't these use dyn_cast? It is isa + cast.

https://github.com/llvm/llvm-project/pull/115626