Fix FS0667: disambiguate cenv record update in IlxGen.fs

The [<AutoOpen>] split brought multiple record types with 'stackGuard'
field into scope (FreeVarOptions, RemapContext, cenv). Add type annotation
to resolve ambiguity.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: T-Gro

src/Compiler/CodeGen/IlxGen.fs

@@ -3208,7 +3208,7 @@ and DelayCodeGenMethodForExpr cenv mgbuf (_, _, eenv, _, _, _, _ as args) =
     let change3rdOutOf7 (a1, a2, _, a4, a5, a6, a7) newA3 = (a1, a2, newA3, a4, a5, a6, a7)
 
     if eenv.delayCodeGen then
-        let cenv =
+        let cenv: cenv =
             { cenv with
                 stackGuard = getEmptyStackGuard ()
             }