tests: modify partial_dependency test to cover a bug

Currently if a dependency is added to declare_dependency, and the top
dependency doesn't have an attribute that the subdependency does, it
wont be propagated by subdependency.

test cases/common/189 partial dependency/declare_dependency/meson.build

@@ -12,9 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+dec_sub_dep = declare_dependency(
+  include_directories : include_directories('headers'),
+)
+
 dec_dep = declare_dependency(
   sources : files('headers/foo.c'),
-  include_directories : include_directories('headers'),
+  dependencies : dec_sub_dep,
 )
 
 sub_dep = dec_dep.partial_dependency(includes : true)