tests: surface-screenshot needs libshared

surface-screenshot-test.c uses file_create_dated() provided by libshared, so it
needs to link libshared.

This was not a problem when unresolved symbols during build were allowed and
the symbols was provided by the weston executable which accidentally exported
all libshared symbols. This would become a problem when we disallow unresolved
symbols project-wide, so fix it.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

tests/meson.build

@@ -184,7 +184,7 @@ tests_weston_plugin = [
 	['plugin-registry'],
 	['surface'],
 	['surface-global'],
-	['surface-screenshot'],
+	['surface-screenshot', 'surface-screenshot-test.c', dep_libshared],
 ]
 
 if get_option('shell-ivi')