fix: make # after alpha/beta optional (googleapis#540)

Author: busunkim96

gapic/schema/naming.py

@@ -99,7 +99,7 @@ def build(
         # This code may look counter-intuitive (why not use ? to make it
         # optional), but the engine's greediness routine will decide that
         # the version is the name, which is not what we want.
-        version = r'\.(?P<version>v[0-9]+(p[0-9]+)?((alpha|beta)[0-9]+)?)'
+        version = r'\.(?P<version>v[0-9]+(p[0-9]+)?((alpha|beta)[0-9]*)?)'
         if re.search(version, root_package):
             pattern += version