Fixes the diffs rendered output being cached in correctly

The rendered output of the diff was getting rendered
and then cached by our safe HTML directive incorrectly.
This fixes that by always adding a key to the part where
safe HTML renders so that it will always re-render
the output.

app/assets/javascripts/diffs/components/inline_diff_table_row.vue

@@ -242,6 +242,7 @@ export default {
       class="line-coverage"
     ></td>
     <td
+      :key="line.line_code"
       v-safe-html="line.rich_text"
       :class="[
         line.type,

app/assets/javascripts/diffs/components/parallel_diff_table_row.vue

@@ -341,6 +341,7 @@ export default {
       <td :class="parallelViewLeftLineType" class="line-coverage left-side"></td>
       <td
         :id="line.left.line_code"
+        :key="line.left.line_code"
         v-safe-html="line.left.rich_text"
         :class="parallelViewLeftLineType"
         class="line_content with-coverage parallel left-side"
@@ -401,6 +402,7 @@ export default {
       ></td>
       <td
         :id="line.right.line_code"
+        :key="line.right.rich_text"
         v-safe-html="line.right.rich_text"
         :class="[
           line.right.type,