SCons: Fix MBEDTLS_CONFIG_FILE string escape

Fixes #30431, regression from #30277.

core/math/SCsub

@@ -22,7 +22,7 @@ if not has_module:
     env_thirdparty = env_math.Clone()
     env_thirdparty.disable_warnings()
     # Custom config file
-    env_thirdparty.Append(CPPDEFINES=[('MBEDTLS_CONFIG_FILE', "thirdparty/mbedtls/include/godot_core_mbedtls_config.h")])
+    env_thirdparty.Append(CPPDEFINES=[('MBEDTLS_CONFIG_FILE', '\\"thirdparty/mbedtls/include/godot_core_mbedtls_config.h\\"')])
     thirdparty_mbedtls_dir = "#thirdparty/mbedtls/library/"
     thirdparty_mbedtls_sources = [
         "aes.c",