[prettier] Ignore compiler/target (facebook#31168)

Add missing directory to prettierignore.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/31168).
* facebook#31167
* facebook#31166
* facebook#31165
* facebook#31164
* facebook#31148
* __->__ facebook#31168

.prettierignore

@@ -24,6 +24,7 @@ compiler/**/.next
 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.todo-kitchensink.js
 
 compiler/crates
+compiler/target
 compiler/apps/playground/public
 
 compiler/**/LICENSE