chore(doc): spelling (#3172)

* Spelling: 'an unicode' -> 'a unicode'

* fix(changelog) spelling

* Remove double spaces

* Spelling

examples/scroll/lv_example_scroll_3.c

@@ -22,7 +22,7 @@ static void float_btn_event_cb(lv_event_t * e)
 }
 
 /**
- * Create a list a with a floating button
+ * Create a list with a floating button
  */
 void lv_example_scroll_3(void)
 {

examples/scroll/lv_example_scroll_3.py

@@ -2,7 +2,7 @@ class ScrollExample_3():
     def __init__(self):
         self.btn_cnt = 1
         #
-        # Create a list a with a floating button
+        # Create a list with a floating button
         #
 
         list = lv.list(lv.scr_act())