Stop duplicating additionaltags for the sle15 container

the code was assuming that first path is always self.name, which is
not the case for the sle15 container as it defines the first path
to be the "extra" compatibility path.

Author: dirkmueller

src/bci_build/package/__init__.py

@@ -1185,9 +1185,11 @@ def kiwi_additional_tags(self) -> str | None:
 
         """
         extra_tags: list[str] = []
-        for buildtag in self.build_tags[1:]:
+        all_tags = self.build_tags
+        first_path = all_tags[0].partition(":")[0]
+        for buildtag in all_tags[1:]:
             path, tag = buildtag.split(":")
-            if path.endswith(self.name):
+            if path.endswith(first_path):
                 extra_tags.append(tag)
 
         return ",".join(extra_tags) if extra_tags else None