Fix #6436: Add regression test

Author: nicolasstucki

tests/neg/i6436.check

@@ -0,0 +1,10 @@
+-- Error: tests/neg/i6436.scala:5:9 ------------------------------------------------------------------------------------
+5 |    case '{ StringContext(${ExprSeq(parts)}: _*) } => // error
+  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |         no implicit argument of type scala.quoted.QuoteContext was found
+-- [E006] Unbound Identifier Error: tests/neg/i6436.scala:6:34 ---------------------------------------------------------
+6 |      val ps: Seq[Expr[String]] = parts // error
+  |                                  ^^^^^
+  |                                  Not found: parts
+
+longer explanation available when compiling with `-explain`

tests/neg/i6436.scala

@@ -0,0 +1,8 @@
+import scala.quoted._
+import scala.quoted.matching._
+def f(sc: quoted.Expr[StringContext]): Unit = {
+  sc match {
+    case '{ StringContext(${ExprSeq(parts)}: _*) } => // error
+      val ps: Seq[Expr[String]] = parts // error
+  }
+}