patch 8.2.1286: Vim9: No error when using a type to a window variable

Problem:    Vim9: No error when using a type to a window variable
Solution:   Recognize the syntax and give an error. (closes #6521)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index bd3de8f..85747d5 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -3324,6 +3324,14 @@
 		return eap->cmd;
 	    }
 	}
+
+	// Recognize using a type for a w:, b:, t: or g: variable:
+	// "w:varname: number = 123".
+	if (eap->cmd[1] == ':' && *p == ':')
+	{
+	    eap->cmdidx = CMD_eval;
+	    return eap->cmd;
+	}
     }
 #endif