Avoid duplicate keys by changing period key

aleksis/apps/lesrooster/frontend/components/timetable_management/timetables/MiniTimeTable.vue

@@ -85,7 +85,7 @@ export default defineComponent({
         gridColumn: 'legend-day',
         gridRow: `period-${period} / span 1`,
       }"
-      :key="period"
+      :key="'period' + period"
     >
       <v-card-text>{{ period }}</v-card-text>
     </v-card>