Lower threshold for 2020 tests (#3030)

* Lower threshold for 2020 tests

Now that the tests zoom into the model and center it before taking a
snapshot, they should be less sensitive.

* Genuine, nontrivial changes to the integration test images

src/wasm-lib/derive-docs/tests/doc_comment_with_code.gen

@@ -88,7 +88,7 @@ mod test_examples_my_func {
         twenty_twenty::assert_image(
             &format!("tests/outputs/{}.png", "serial_test_example_my_func0"),
             &actual,
-            1.0,
+            0.99,
         );
     }
 
@@ -178,7 +178,7 @@ mod test_examples_my_func {
         twenty_twenty::assert_image(
             &format!("tests/outputs/{}.png", "serial_test_example_my_func1"),
             &actual,
-            1.0,
+            0.99,
         );
     }
 }