Fix build with gcc-16.

deadbeef's action callback2 takes ddb_action_context_t (not const int)
as of DDB_API_LEVEL 11; gcc-16 hard-errors the incompatible-pointer-types
assignment. Correct the three action callback signatures. Upstream
inactive since 2017.
--- a/opus.c
+++ b/opus.c
@@ -1644,13 +1644,13 @@
     deadbeef->plt_unref(plt);
 }
 
-static int opus_embed_pics(DB_plugin_action_t *action, const int ctx)
+static int opus_embed_pics(DB_plugin_action_t *action, ddb_action_context_t ctx)
 {
     for_all_selected(embed_album_art);
     return 0;
 }
 
-static int opus_save_streams(DB_plugin_action_t *action, const int ctx)
+static int opus_save_streams(DB_plugin_action_t *action, ddb_action_context_t ctx)
 {
     char *pattern = copy_conf_str("opus.opusname");
     for_all_selected(save_file, pattern && pattern[0] ? pattern : "%n-%t.opus", false);
@@ -1658,7 +1658,7 @@
     return 0;
 }
 
-static int opus_save_links(DB_plugin_action_t *action, const int ctx)
+static int opus_save_links(DB_plugin_action_t *action, ddb_action_context_t ctx)
 {
     char *pattern = copy_conf_str("opus.oggname");
     for_all_selected(save_file, pattern && pattern[0] ? pattern : "%n-%t.opus", true);