Build maintenance and bug fix

* Attempt fixing Linux build, broke after switching to enet6.

* Upgrade unordered_dense to 73f3cbb237e84d483afafc743f1f14ec53e12314

* Fix sound_default_mixer being applied upon sound load even if that sound was set to a custom mixer before hand.

SConstruct

@@ -52,7 +52,7 @@ elif env["PLATFORM"] == "posix":
 	# enable the gold linker to silence seemingly pointless warnings about symbols in the bass libraries, strip the resulting binaries, and add /usr/local/lib to the libpath because it seems we aren't finding libraries unless we do manually.
 	env.Append(CPPPATH = ["/usr/local/include"], LIBPATH = ["/usr/local/lib"], LINKFLAGS = ["-fuse-ld=gold", "-g" if ARGUMENTS.get("debug", 0) == "1" else "-s"])
 	# We must explicitly denote the static linkage for several libraries or else gcc will choose the dynamic ones.
-	env.Append(LIBS = [":libangelscript.a", ":libenet.a", ":libSDL3.a", "crypto", "ssl"])
+	env.Append(LIBS = [":libangelscript.a", ":libenet6.a", ":libSDL3.a", "crypto", "ssl"])
 env.Append(CPPDEFINES = ["POCO_STATIC", "UNIVERSAL_SPEECH_STATIC", "DEBUG" if ARGUMENTS.get("debug", "0") == "1" else "NDEBUG", "UNICODE"])
 env.Append(CPPPATH = ["#ASAddon/include", "#dep"], LIBPATH = ["#build/lib"])