Regex match nextcloud version to avoid pulling versions like `26` or `26.0` (#1067)

library/ix-dev/charts/nextcloud/upgrade_strategy

@@ -1,19 +1,23 @@
 #!/usr/bin/python3
 import json
+import re
 import sys
 
 from catalog_update.upgrade_strategy import semantic_versioning
 
 
+RE_STABLE_VERSION = re.compile(r'^[0-9]+\.[0-9]+\.[0-9]+$')
+
+
 def newer_mapping(image_tags):
     key = list(image_tags.keys())[0]
-    # 21.1 is greater then 21.1.0 so we reverse sort bfeore doing semantic versioning
-    version = semantic_versioning(sorted(image_tags[key], reverse=True))
+    tags = {t: t for t in image_tags[key] if RE_STABLE_VERSION.fullmatch(t)}
+    version = semantic_versioning(list(tags))
     if not version:
         return {}
 
     return {
-        'tags': {key: version},
+        'tags': {key: tags[version]},
         'app_version': version,
     }