patch 9.0.0063: too many type casts for dict_get functions

Problem:    Too many type casts for dict_get functions.
Solution:   Change the key argument from "char_u *" to "char *".
diff --git a/src/dict.c b/src/dict.c
index d281957..29608bd 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -662,11 +662,11 @@
  * Returns FAIL if the entry doesn't exist or out of memory.
  */
     int
-dict_get_tv(dict_T *d, char_u *key, typval_T *rettv)
+dict_get_tv(dict_T *d, char *key, typval_T *rettv)
 {
     dictitem_T	*di;
 
-    di = dict_find(d, key, -1);
+    di = dict_find(d, (char_u *)key, -1);
     if (di == NULL)
 	return FAIL;
     copy_tv(&di->di_tv, rettv);
@@ -680,12 +680,12 @@
  * Returns NULL if the entry doesn't exist or out of memory.
  */
     char_u *
-dict_get_string(dict_T *d, char_u *key, int save)
+dict_get_string(dict_T *d, char *key, int save)
 {
     dictitem_T	*di;
     char_u	*s;
 
-    di = dict_find(d, key, -1);
+    di = dict_find(d, (char_u *)key, -1);
     if (di == NULL)
 	return NULL;
     s = tv_get_string(&di->di_tv);
@@ -699,7 +699,7 @@
  * Returns 0 if the entry doesn't exist.
  */
     varnumber_T
-dict_get_number(dict_T *d, char_u *key)
+dict_get_number(dict_T *d, char *key)
 {
     return dict_get_number_def(d, key, 0);
 }
@@ -709,11 +709,11 @@
  * Returns "def" if the entry doesn't exist.
  */
     varnumber_T
-dict_get_number_def(dict_T *d, char_u *key, int def)
+dict_get_number_def(dict_T *d, char *key, int def)
 {
     dictitem_T	*di;
 
-    di = dict_find(d, key, -1);
+    di = dict_find(d, (char_u *)key, -1);
     if (di == NULL)
 	return def;
     return tv_get_number(&di->di_tv);
@@ -745,11 +745,11 @@
  * Returns "def" if the entry doesn't exist.
  */
     varnumber_T
-dict_get_bool(dict_T *d, char_u *key, int def)
+dict_get_bool(dict_T *d, char *key, int def)
 {
     dictitem_T	*di;
 
-    di = dict_find(d, key, -1);
+    di = dict_find(d, (char_u *)key, -1);
     if (di == NULL)
 	return def;
     return tv_get_bool(&di->di_tv);