bug symfony#27286 [Translation] Add Occitan plural rule (kylekatarnls)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes symfony#27286).

Discussion
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[Translation] Add Occitan plural rule

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Enable correct plural on Occitan translations. Could be safely merged in versions branches.

Commits
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0de3a61 Add Occitan plural rule

Author: fabpot

src/Symfony/Component/Translation/PluralizationRules.php

@@ -107,6 +107,7 @@ public static function get($number, $locale)
             case 'nl':
             case 'nn':
             case 'no':
+            case 'oc':
             case 'om':
             case 'or':
             case 'pa':