TextureTools: add some fuzziness to DistanceField test comparison.

src/Magnum/TextureTools/Test/DistanceFieldGLTest.cpp

@@ -198,7 +198,11 @@ void DistanceFieldGLTest::test() {
 
     CORRADE_COMPARE_WITH(*actualOutputImage,
         Utility::Directory::join(_testDir, "output.tga"),
-        DebugTools::CompareImageToFile{_manager});
+        /* Some mobile GPUs have slight (off-by-one) rounding errors compared
+           to the ground truth, but it's just a very small amount of pixels
+           (20-50 out of the total 4k pixels). That's okay. It's also possible
+           that the ground truth itself has rounding errors ;) */
+        (DebugTools::CompareImageToFile{_manager, 1.0f, 0.0125f}));
 }
 
 #ifndef MAGNUM_TARGET_WEBGL