test: Allow optional usage of vendored googletest

Change-Id: I7011edb826b11762f1eb49e8bbc3a19c8006f8c5
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meson.build b/meson.build
index ae1e2c6..f23dec5 100644
--- a/meson.build
+++ b/meson.build
@@ -1,5 +1,5 @@
 project('sdeventplus', 'cpp',
-        version: '0.1', meson_version: '>=0.49.0',
+        version: '0.1', meson_version: '>=0.53.2',
         default_options: [
           'warning_level=3',
           'werror=true',