Actually match the tag naming conventions (#6393)

Wasn't matching on release candidates, nor any of the previous special tags convention.

Author: mjjbell

.github/workflows/osrm-backend.yml

@@ -5,7 +5,7 @@ on:
       - master
     tags:
       - v[1-9]+.[0-9]+.[0-9]+
-      - v[1-9]+.[0-9]+.[0-9]+-[0-9a-zA-Z]+
+      - v[1-9]+.[0-9]+.[0-9]+-[a-zA-Z]+.[0-9]+
       - v[1-9]+.[0-9]+-[0-9a-zA-Z]+
   pull_request:
     branches: