build: Move Meson dependency() calls to where they’re used

This avoids making the project depend on all its dependencies, some of
which are optional, when being built as a Meson subproject.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

src/tests/meson.build

@@ -116,9 +116,9 @@ if get_option('enable_gtk')
   test_ui_deps = [
     libsysprof_dep,
     libsysprof_ui_dep,
-    gtk_dep,
-    dazzle_dep,
-    pangoft2_dep,
+    dependency('gtk+-3.0', version: gtk_req_version),
+    dependency('libdazzle-1.0', version: dazzle_req_version, fallback: ['libdazzle', 'libdazzle_dep']),
+    dependency('pangoft2', required: false),
   ]
 
   test_model_filter = executable('test-model-filter', 'test-model-filter.c',