scripts/build-unit-test-docker: Update googletest to match poky

googletest doesn't regularly tag releases even though they are
constantly making improvements. The source is now 2 years old and the
yocto poky build has moved on to this commit.

Change-Id: I867ead5f89fecc9c854626cd07fc8d1a6a9cc5af
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 7df74c7..c44c1eb 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -124,10 +124,11 @@
             f"cp include/function2/function2.hpp {prefix}/include/function2/",
         ],
     ),
+    # Snapshot from 2021-05-13
     "google/googletest": PackageDef(
-        rev="release-1.10.0",
+        rev="662fe38e44900c007eccb65a5d2ea19df7bd520e",
         build_type="cmake",
-        config_env=["CXXFLAGS=-std=c++17"],
+        config_env=["CXXFLAGS=-std=c++20"],
         config_flags=["-DTHREADS_PREFER_PTHREAD_FLAG=ON"],
     ),
     # Release 2020-08-06