Fix gitignore so ripgrep works

ripgrep was failing to search in the bindgen repo:
```
./.gitignore: line 19: error parsing glob '**.orig': invalid use of **; must be one path component
```

Per the gitignore docs it seems like ripgrep is correct and this line is
invalid: https://git-scm.com/docs/gitignore#_pattern_format

Author: luser

.gitignore

@@ -16,4 +16,4 @@ __bindgen.*
 csmith-fuzzing/platform.info
 
 # Backups of test cases from C-Reduce
-**.orig
+**/*.orig