The MUSIC_* flags aren't exposed to Lua
Despite the MusicChange hook and global constant mapmusflags now being in Lua, the MUSIC_* constants they use, being MUSIC_TRACKMASK, MUSIC_RELOADRESET, and MUSIC_FORCERESET are still not exposed to Lua.
On the wiki, the description for the MusicChange hook tells you to use these constants despite them not existing in Lua:
And for mapmusflags, the description just tells you to use magic hex numbers instead of the proper constants: