meson: Disable tests build for tinyxml2 dependency

Currently local meson build breaks on tinyxml2 since the code from
this package produces a warning and all warnings are treated as errors:
"""
../subprojects/tinyxml2-9.0.0/xmltest.cpp:711:38: error: ignoring
return value of ‘char* fgets(char*, int, FILE*)’ declared with
attribute ‘warn_unused_result’ [-Werror=unused-result]
"""
The warning above comes from the compilation of the tinyxml2 unit tests.
Since we don't really need them, disable 'tests' option for tinyxml2
dependency to fix the meson build.

Tested:
Locally executed "meson setup build && cd build && meson compile" now
finishes successfully.

Change-Id: I7148856a3eebbda22d03c9715955b6ab78a933fe
Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
diff --git a/meson.build b/meson.build
index 04906fa..9e84fa9 100644
--- a/meson.build
+++ b/meson.build
@@ -298,6 +298,7 @@
     'tinyxml2',
     include_type: 'system',
     version: '>=9.0.0',
+    default_options: ['tests=false'],
 )
 if not tinyxml.found()
     tinyxml_proj = subproject('tinyxml2', required: true)