[IndexTable.Row] Revert selectable=false early return, which break on… (

Shopify#11773)

### WHAT is this pull request doing?

This PR reverts a change made in Shopify#11763, unrelated to the bug fixed,
that caused an unintended regression: breaking `onNavigation` behavior
for unselectable tables. This needs to ship in a patch asap because it
is live in v12.20.0.

.changeset/real-papayas-tease.md

@@ -0,0 +1,5 @@
+---
+'@shopify/polaris': patch
+---
+
+Reverted a change that caused `IndexTable` `onNavigation` not to work when `selectable` is `false`

polaris-react/src/components/IndexTable/components/Row/Row.tsx

@@ -142,7 +142,7 @@ export const Row = memo(function Row({
         return;
       }
 
-      if (primaryLinkElement.current && !selectMode && selectable) {
+      if (primaryLinkElement.current && !selectMode) {
         isNavigating.current = true;
         const {ctrlKey, metaKey} = event.nativeEvent;