fix: support lowercase .appimage in asset filtering

Author: Cyber-Syntax

my_unicorn/github_client.py

@@ -293,7 +293,7 @@ def extract_appimage_asset(self, release_data: GitHubReleaseDetails) -> GitHubAs
 
         """
         for asset in release_data["assets"]:
-            if asset["name"].endswith(".AppImage"):
+            if asset["name"].endswith(".AppImage") or asset["name"].endswith(".appimage"):
                 return asset
         return None
 
@@ -308,7 +308,9 @@ def extract_appimage_assets(self, release_data: GitHubReleaseDetails) -> list[Gi
 
         """
         return [
-            asset for asset in release_data["assets"] if asset["name"].endswith(".AppImage")
+            asset
+            for asset in release_data["assets"]
+            if asset["name"].endswith(".AppImage") or asset["name"].endswith(".appimage")
         ]
 
     def select_best_appimage(