patch 9.0.0250: slightly inconsistent error messages

Problem:    Slightly inconsistent error messages.
Solution:   Make it "Using a Float". (closes #10959)
diff --git a/src/errors.h b/src/errors.h
index 99682e4..940d055 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -2054,7 +2054,7 @@
 EXTERN char e_using_float_as_number[]
 	INIT(= N_("E805: Using a Float as a Number"));
 EXTERN char e_using_float_as_string[]
-	INIT(= N_("E806: Using Float as a String"));
+	INIT(= N_("E806: Using a Float as a String"));
 #endif
 #ifdef FEAT_FLOAT
 EXTERN char e_expected_float_argument_for_printf[]