Adjust includes to use <> instead of "", consistent with quickstart pages.

Right now, gtest documentation uses different #include syntax. The quickstart
pages (e.g., http://google.github.io/googletest/quickstart-bazel.html#create-and-run-a-binary) are checked in with `#include <gtest/gtest.h>` However, other
documentation (such as the primer) uses `#include "gtest/gtest.h"` (e.g.,
https://google.github.io/googletest/primer.html#writing-the-main-function).

PiperOrigin-RevId: 551878641
Change-Id: Iab93cc1da3ef4870a07b624071b75d6e9d3568c1

docs/gmock_cheat_sheet.md

@@ -20,7 +20,7 @@ class Foo {
 (note that `~Foo()` **must** be virtual) we can define its mock as
 
 ```cpp
-#include "gmock/gmock.h"
+#include <gmock/gmock.h>
 
 class MockFoo : public Foo {
  public: