Force the server target filename

The server path may be customized using SCRCPY_APK. If its basename is
different from "scrcpy.apk", it will be pushed with a different name,
so the execution would fail.

Therefore, force the push target filename.

app/src/server.c

@@ -11,7 +11,7 @@ process_t push_server(const char *serial) {
     if (!apk_path) {
         apk_path = "scrcpy.apk";
     }
-    return adb_push(serial, apk_path, "/data/local/tmp/");
+    return adb_push(serial, apk_path, "/data/local/tmp/scrcpy.apk");
 }
 
 process_t enable_tunnel(const char *serial, Uint16 local_port) {