fix: test issue (probably) caused by application start order

After adding `emqx_rule_engine` to the `app.src` file for
`emqx_ee_schema_registry` the test suites in `emqx_ee_schema_registry`
started to fail when they where run together with
`make "lib-ee/emqx_ee_schema_registry-ct"`. However, they still worked
when executed one by one with
`SUITE=lib-ee/emqx_ee_schema_registry/test/emqx_ee_schema_registry_http_api_SUITE.erl make ct-suite`.
The failure probably happened as this changed the application start
order. As `emqx_ee_schema_registry` only requires `emqx_rule_engine` to be
loaded, `emqx_rule_engine` can be put in the included_applications list in
the emqx_ee_schema_registry.app.src file instead (this solved the issue).

lib-ee/emqx_ee_schema_registry/src/emqx_ee_schema_registry.app.src

@@ -3,12 +3,14 @@
     {vsn, "0.1.5"},
     {registered, [emqx_ee_schema_registry_sup]},
     {mod, {emqx_ee_schema_registry_app, []}},
+    {included_applications, [
+        emqx_rule_engine
+    ]},
     {applications, [
         kernel,
         stdlib,
         erlavro,
-        gpb,
-        emqx_rule_engine
+        gpb
     ]},
     {env, []},
     {modules, []},

lib-ee/emqx_ee_schema_registry/test/emqx_ee_schema_registry_SUITE.erl

@@ -814,7 +814,7 @@ t_sparkplug_decode(_Config) ->
     ?assertMatch(#{data := ExpectedRuleOutput}, Res),
     ok.
 
-t_sparkplug_encode(Config) ->
+t_sparkplug_encode(_Config) ->
     %% Default message name field is 'Payload'
     SQL =
         <<