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

compiler/testData/diagnostics/tests/inference/nullableUpperBound.fir.kt

@@ -0,0 +1,9 @@
+package o
+
+fun foo(): String? {
+    return accept(JV<String?, Unit?>())
+}
+
+fun <R, D> accept(v: JV<R, D>): R? = null
+
+open class JV<R, D>()