Use consistent extension icon URLs

Better caching between versions.

(cherry picked from commit 30f845139d)

app/src/main/java/eu/kanade/tachiyomi/extension/api/ExtensionGithubApi.kt

@@ -117,7 +117,7 @@ internal class ExtensionGithubApi {
                     hasChangelog = it.hasChangelog == 1,
                     sources = it.sources?.toExtensionSources() ?: emptyList(),
                     apkName = it.apk,
-                    iconUrl = "${getUrlPrefix()}icon/${it.apk.replace(".apk", ".png")}",
+                    iconUrl = "${getUrlPrefix()}icon/${it.pkg}.png",
                 )
             }
     }