Adjusts syntax tests to read-only array length.

test/libsolidity/syntaxTests/array/push/calldata_push.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f(uint[] calldata x) external {
+        x.push();
+    }
+}
+// ----
+// TypeError: (66-72): Member "push" is not available in uint256[] calldata outside of storage.

test/libsolidity/syntaxTests/array/push/memory_push.sol

@@ -0,0 +1,8 @@
+contract C {
+    function f() public {
+        uint[] memory x;
+        x.push();
+    }
+}
+// ----
+// TypeError: (72-78): Member "push" is not available in uint256[] memory outside of storage.