Fix typos in code and docs with codespell

Using v1.11.0 from https://github.com/lucasdemarchi/codespell

core/script_language.h

@@ -179,7 +179,7 @@ class ScriptCodeCompletionCache {
 public:
 	virtual RES get_cached_resource(const String &p_path) = 0;
 
-	static ScriptCodeCompletionCache *get_sigleton() { return singleton; }
+	static ScriptCodeCompletionCache *get_singleton() { return singleton; }
 
 	ScriptCodeCompletionCache();
 };