patch 8.2.3197: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move a few more error messages to errors.h.
diff --git a/src/evalvars.c b/src/evalvars.c
index 909ee1d..c58f734 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -2232,7 +2232,7 @@
     // VV_RO is also checked when compiling, but let's check here as well.
     if (vimvars[idx].vv_flags & VV_RO)
     {
-	semsg(_(e_readonlyvar), vimvars[idx].vv_name);
+	semsg(_(e_cannot_change_readonly_variable_str), vimvars[idx].vv_name);
 	return FAIL;
     }
     if (sandbox && (vimvars[idx].vv_flags & VV_RO_SBX))
@@ -3499,7 +3499,8 @@
 {
     if (flags & DI_FLAGS_RO)
     {
-	semsg(_(e_readonlyvar), use_gettext ? (char_u *)_(name) : name);
+	semsg(_(e_cannot_change_readonly_variable_str),
+				       use_gettext ? (char_u *)_(name) : name);
 	return TRUE;
     }
     if ((flags & DI_FLAGS_RO_SBX) && sandbox)