[Test] Add regression test.

For #70234 (comment) .

Author: nate-chandler

test/SILOptimizer/consume_operator_kills_copyable_loadable_vars.swift

@@ -723,6 +723,12 @@ func consumeInitdArray() {
   _ = consume x
 }
 
+func isNegative(_ c: consuming Int) -> Bool { return c < 0 }
+func consumeInt() {
+    var g = 0 // expected-warning{{variable 'g' was never mutated; consider changing to 'let' constant}}
+    isNegative(consume g) // expected-warning{{result of call to 'isNegative' is unused}}
+}
+
 //////////////////////
 // Reinit in pieces //
 //////////////////////