patch 8.2.1746: Vim9: cannot use "fina" for "finally"

Problem:    Vim9: Cannot use "fina" for "finally". (Naruhiko Nishino)
Solution:   Specifically check for "fina". (closes #7020)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index a7542f3..bb504ff 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -3420,6 +3420,10 @@
 	    eap->cmdidx = CMD_SIZE;
     }
 
+    // ":fina" means ":finally" for backwards compatibility.
+    if (eap->cmdidx == CMD_final && p - eap->cmd == 4)
+	eap->cmdidx = CMD_finally;
+
     return p;
 }