Fix splice type variable pattern detection

Fixes #17039

Author: nicolasstucki

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

@@ -249,7 +249,7 @@ trait QuotesAndSplices {
             val pat1 = if (patType eq patType1) pat else pat.withType(patType1)
             patBuf += pat1
           }
-        case Select(pat, _) if tree.symbol.isTypeSplice =>
+        case Select(pat: Bind, _) if tree.symbol.isTypeSplice =>
           val sym = tree.tpe.dealias.typeSymbol
           if sym.exists then
             val tdef = TypeDef(sym.asType).withSpan(sym.span)

tests/pos-macros/i17039.scala

@@ -0,0 +1,7 @@
+import scala.quoted.*
+
+def macroImpl(using Quotes) =
+  val t = summon[Type[Int]]
+  Type.of[Int] match
+    case '[t.Underlying] => '{true}
+    case _ => '{false}