Convert CharSequences to Strings explicitly.

The Scala 3 compiler reports an error:

```scala
-- [E008] Not Found Error: /Users/matt/scalasql/scalasql/core/src/SqlStr.scala:53:33
53 |            if (castParams) part + s"CAST(? AS $jdbcTypeString)" else part + "?"
   |                            ^^^^^^
   |value + is not a member of CharSequence, but could be made available as an extension method.
   |
   |One of the following imports might make progress towards fixing the problem:
   |
   |  import scala.math.Fractional.Implicits.infixFractionalOps
   |  import scala.math.Integral.Implicits.infixIntegralOps
   |  import scala.math.Numeric.Implicits.infixNumericOps
   |  import sourcecode.Text.generate
```

Author: mrdziuban

scalasql/core/src/SqlStr.scala

@@ -50,7 +50,7 @@ object SqlStr {
           case (part, null) => part
           case (part, param) =>
             val jdbcTypeString = param.mappedType.castTypeString
-            if (castParams) part + s"CAST(? AS $jdbcTypeString)" else part + "?"
+            if (castParams) part.toString + s"CAST(? AS $jdbcTypeString)" else part.toString + "?"
         }
         .mkString