Don't use localized numbers for downloaded image filenames

Probably fixes #10258

(cherry picked from commit 19f0175a56b00afd772d5d0c4909c49371a59bbe)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/data/download/Downloader.kt
#	core/src/main/java/tachiyomi/core/util/system/ImageUtil.kt

core/src/main/java/tachiyomi/core/util/system/ImageUtil.kt

@@ -37,6 +37,7 @@ import java.io.File
 import java.io.InputStream
 import java.net.URLConnection
 import java.security.SecureRandom
+import java.util.Locale
 import kotlin.math.abs
 import kotlin.math.max
 import kotlin.math.min
@@ -366,6 +367,7 @@ object ImageUtil {
     }
 
     private fun splitImageName(filenamePrefix: String, index: Int) = "${filenamePrefix}__${"%03d".format(
+        Locale.ENGLISH,
         index + 1,
     )}.jpg"