Fix #8894: Add regression test

It was fixed in #8884

Author: nicolasstucki

tests/neg/i8894.scala

@@ -0,0 +1,13 @@
+trait Extractor {
+  inline def unapplySeq(inline tn: String): Option[Seq[String]]
+}
+
+transparent inline def (inline sc: StringContext).poql: Extractor = new Extractor {
+  inline def unapplySeq(inline tn: String): Option[Seq[String]] = ??? // error: Implementation restriction: nested inline methods are not supported
+}
+
+object x {
+  "x" match {
+    case poql" $x" => x // error: Deferred inline method unapplySeq in trait Extractor cannot be invoked
+  }
+}