Date text encoding includes leading zero for month and day

e.g. 2000-01-01 instead of 2000-1-1. PostgreSQL accepted it without
zeroes but our text decoder didn't. This caused a problem when we needed
to take a value and encode to text so something else could parse it as
if it had come from the PostgreSQL server in text format. e.g.
database/sql compatibility.

pgtype/date.go

@@ -195,8 +195,14 @@ func (encodePlanDateCodecText) Encode(value any, buf []byte) (newBuf []byte, err
 
 		buf = strconv.AppendInt(buf, int64(year), 10)
 		buf = append(buf, '-')
+		if date.Time.Month() < 10 {
+			buf = append(buf, '0')
+		}
 		buf = strconv.AppendInt(buf, int64(date.Time.Month()), 10)
 		buf = append(buf, '-')
+		if date.Time.Day() < 10 {
+			buf = append(buf, '0')
+		}
 		buf = strconv.AppendInt(buf, int64(date.Time.Day()), 10)
 
 		if bc {