[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/tests/smartCasts/inference/dependentOnPrevArg.fir.kt

@@ -0,0 +1,7 @@
+package a
+
+fun <T> foo(u: T, v: T): T = u
+
+fun test(s: String?) {
+    val r: String = foo(s!!, s)
+}