patch 8.2.4886: Vim9: redir in skipped block seen as assignment

Problem:    Vim9: redir in skipped block seen as assignment.
Solution:   Check for valid assignment.

src/ex_docmd.c

@@ -3683,6 +3683,7 @@ find_ex_command(
 	    // "&opt = expr"
 	    // "var = expr"  where "var" is a variable name or we are skipping
 	    // (variable declaration might have been skipped).
+	    // Not "redir => var" (when skipping).
 	    oplen = assignment_len(skipwhite(p), &heredoc);
 	    if (oplen > 0)
 	    {
@@ -3690,7 +3691,8 @@ find_ex_command(
 			|| *eap->cmd == '&'
 			|| *eap->cmd == '$'
 			|| *eap->cmd == '@'
-			|| eap->skip
+			|| (eap->skip && IS_WHITE_OR_NUL(
+						      *(skipwhite(p) + oplen)))
 			|| lookup(eap->cmd, p - eap->cmd, TRUE, cctx) == OK)
 		{
 		    eap->cmdidx = CMD_var;