avoid infix with _*. prepare Scala 3

https://github.com/playframework/playframework/blob/6e614d11cca8070e6c3aa4940f682f8cc1183e73/core/play/src/main/scala/play/api/libs/typedmap/TypedMap.scala#L94

```
[error] 99 |    withAttrs(attrs + (entries: _*))
[error]    |                                ^
[error]    |          `_*` can be used only for last argument of method application.
[error]    |          It is no longer allowed in operands of infix operations.
```

```
Welcome to Scala 3.1.2 (11.0.15, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> object A { def +(xs: Int*): Unit = () }
// defined object A

scala> def a(xs: Int*) = A + (xs: _*)
-- Error: ----------------------------------------------------------------------
1 |def a(xs: Int*) = A + (xs: _*)
  |                           ^
  |            `_*` can be used only for last argument of method application.
  |            It is no longer allowed in operands of infix operations.

scala> def a(xs: Int*) = A.+(xs: _*)
def a(xs: Int*): Unit
```

core/play/src/main/scala/play/api/mvc/Request.scala

@@ -96,7 +96,7 @@ trait Request[+A] extends RequestHeader {
   override def addAttrs(e1: TypedEntry[_], e2: TypedEntry[_], e3: TypedEntry[_]): Request[A] =
     withAttrs(attrs + (e1, e2, e3))
   override def addAttrs(entries: TypedEntry[_]*): Request[A] =
-    withAttrs(attrs + (entries: _*))
+    withAttrs(attrs.+(entries: _*))
   override def removeAttr(key: TypedKey[_]): Request[A] =
     withAttrs(attrs - key)
   override def withTransientLang(lang: Lang): Request[A] =

core/play/src/main/scala/play/api/mvc/RequestHeader.scala

@@ -186,7 +186,7 @@ trait RequestHeader {
    * @return The new version of this object with the new attributes.
    */
   def addAttrs(entries: TypedEntry[_]*): RequestHeader =
-    withAttrs(attrs + (entries: _*))
+    withAttrs(attrs.+(entries: _*))
 
   /**
    * Create a new versions of this object with the given attribute removed.

core/play/src/main/scala/play/api/mvc/Results.scala

@@ -429,7 +429,7 @@ case class Result(
    * @return The new version of this object with the new attributes.
    */
   def addAttrs(entries: TypedEntry[_]*): Result =
-    withAttrs(attrs + (entries: _*))
+    withAttrs(attrs.+(entries: _*))
 
   /**
    * Create a new versions of this object with the given attribute removed.