[sensorthings] Fix provider does not work with oauth2 config method

The provider was incorrectly retrieving the authcfg id key from
the layer URI

Fixes #60407

src/core/providers/sensorthings/qgssensorthingsshareddata.cpp

@@ -96,8 +96,7 @@ QgsSensorThingsSharedData::QgsSensorThingsSharedData( const QString &uri )
     mGeometryType = Qgis::WkbType::NoGeometry;
   }
 
-  QgsDataSourceUri dsUri;
-  dsUri.setEncodedUri( uri );
+  const QgsDataSourceUri dsUri( uri );
   mAuthCfg = dsUri.authConfigId();
   mHeaders = dsUri.httpHeaders();