Update tests for interface inheritance

test/libsolidity/semanticTests/interface_inheritance_conversions.sol

@@ -0,0 +1,39 @@
+interface Parent {
+    function parentFun() external returns (uint256);
+}
+
+interface SubA is Parent {
+    function subAFun() external returns (uint256);
+}
+
+interface SubB is Parent {
+    function subBFun() external returns (uint256);
+}
+
+contract Impl is SubA, SubB {
+    function parentFun() override external returns (uint256) { return 1; }
+    function subAFun() override external returns (uint256) { return 2; }
+    function subBFun() override external returns (uint256) { return 3; }
+}
+
+contract C {
+    function convertParent() public returns (uint256) {
+        Parent p = new Impl();
+        return p.parentFun();
+    }
+
+    function convertSubA() public returns (uint256, uint256) {
+        SubA sa = new Impl();
+        return (sa.parentFun(), sa.subAFun());
+    }
+
+    function convertSubB() public returns (uint256, uint256) {
+        SubB sb = new Impl();
+        return (sb.parentFun(), sb.subBFun());
+    }
+}
+
+// ----
+// convertParent() -> 1
+// convertSubA() -> 1, 2
+// convertSubB() -> 1, 3