refactor: Migrate Vue slots to the new syntax (#4603)

Co-authored-by: Alex Grozav <alex@grozav.com>

packages/editor-ui/src/components/MainSidebar.vue

@@ -32,11 +32,13 @@
 						<el-dropdown :disabled="!isCollapsed" placement="right-end" trigger="click" @command="onUserActionToggle">
 							<div :class="{[$style.avatar]: true, ['clickable']: isCollapsed }">
 								<n8n-avatar :firstName="usersStore.currentUser.firstName" :lastName="usersStore.currentUser.lastName" size="small" />
-								<el-dropdown-menu slot="dropdown">
+							</div>
+							<template #dropdown>
+								<el-dropdown-menu>
 									<el-dropdown-item command="settings">{{ $locale.baseText('settings') }}</el-dropdown-item>
 									<el-dropdown-item command="logout">{{ $locale.baseText('auth.signout') }}</el-dropdown-item>
 								</el-dropdown-menu>
-							</div>
+							</template>
 						</el-dropdown>
 					</div>
 					<div :class="{ ['ml-2xs']: true, [$style.userName]: true, [$style.expanded]: fullyExpanded }">