testsuite: Set NO_AT_BRIDGE for gtk tests

The a11y stack insists on spewing hard to control warnings
that make our tests fail. So, no accessibility for gtk tests :(

testsuite/gtk/meson.build

@@ -115,6 +115,7 @@ foreach t : tests
               'GDK_DEBUG=default-settings',
               'GTK_CSD=1',
               'G_ENABLE_DIAGNOSTIC=0',
+              'NO_AT_BRIDGE=1',
               'GSK_RENDERER=cairo',
               'G_TEST_SRCDIR=@0@'.format(meson.current_source_dir()),
               'G_TEST_BUILDDIR=@0@'.format(meson.current_build_dir()),