[FIR] Fix incorrect context usages with withSuppressedDiagnostics call

compiler/testData/diagnostics/tests/suppress/oneWarning/suppressOnDeclarationItself.kt

@@ -0,0 +1,7 @@
+// FIR_IDENTICAL
+
+class A {
+    @Suppress("NOTHING_TO_OVERRIDE")
+    override fun foo() {}
+}
+

compiler/testData/diagnostics/tests/suppress/oneWarning/suppressOnDeclarationItself.txt

@@ -0,0 +1,9 @@
+package
+
+public final class A {
+    public constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    @kotlin.Suppress(names = {"NOTHING_TO_OVERRIDE"}) public open fun foo(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}