Fix Constant tag of Expr(null: String)

Co-authored-by: Hamza Remmal <hamza@remmal.net>
Co-authored-by: HarrisL2 <harris.yh.lau@gmail.com>
Co-authored-by: Abdullah Arif Jafri <abdullahjafri2001@gmail.com>

Author: 4 people

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -2529,7 +2529,8 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
     end StringConstantTypeTest
 
     object StringConstant extends StringConstantModule:
-      def apply(x: String): StringConstant = dotc.core.Constants.Constant(x)
+      def apply(x: String): StringConstant =
+        dotc.core.Constants.Constant(x: Any)
       def unapply(constant: StringConstant): Some[String] = Some(constant.stringValue)
     end StringConstant