SCons: Fix wrong `debug_symbols` default value in --help

The actual default value is neither true nor false but depends on the value
of `dev_build`.
Fixes #71812.

SConstruct

@@ -172,7 +172,7 @@ opts.Add(
         "optimize", "Optimization level", "speed_trace", ("none", "custom", "debug", "speed", "speed_trace", "size")
     )
 )
-opts.Add(BoolVariable("debug_symbols", "Build with debugging symbols", True))
+opts.Add(BoolVariable("debug_symbols", "Build with debugging symbols", False))
 opts.Add(BoolVariable("separate_debug_symbols", "Extract debugging symbols to a separate file", False))
 opts.Add(EnumVariable("lto", "Link-time optimization (production builds)", "none", ("none", "auto", "thin", "full")))
 opts.Add(BoolVariable("production", "Set defaults to build Godot for use in production", False))