fix(build) add missed jquery slim imports

modules/proxyconnection/ProxyConnectionService.js

-/* globals $ */
-
 import { getLogger } from '@jitsi/logger';
+import $ from 'jquery';
 import { $iq } from 'strophe.js';
 
 import { MediaType } from '../../service/RTC/MediaType';

modules/sdp/SDP.spec.js

-/* globals $ */
+import $ from 'jquery';
 import { $iq } from 'strophe.js';
 
 import FeatureFlags from '../flags/FeatureFlags';