Fix warnings for a missing base class and pointer mismatch

[jszumski]

Fixes warnings for a missing base case:

tests/macos/xcodeproj/NonArcObject.h:1:12: warning: class 'NonArcObject' defined without specifying a base class [-Wobjc-root-class]
@interface NonArcObject
           ^
tests/macos/xcodeproj/NonArcObject.h:1:24: note: add a super class to fix this problem
@interface NonArcObject

and a pointer mismatch:

tools/xctest_absolute_source_locations/xctest_absolute_source_locations.m:39:44: warning: incompatible pointer types passing 'NSString *' to parameter of type 'NSURL *' [-Wincompatible-pointer-types]
    NSURL *workspaceURL = getWorkspacePath(testBundlePath);
                                           ^~~~~~~~~~~~~~
tools/xctest_absolute_source_locations/xctest_absolute_source_locations.m:14:39: note: passing argument to parameter 'testBundle' here
static NSURL *getWorkspacePath(NSURL *testBundle)