Add regression test

Fixes #15475

tests/pos-macros/i15475.scala

@@ -0,0 +1,13 @@
+def test =
+  transform {
+    val a: Seq[Generic[?]] = ???
+    a.foreach { to =>
+      to.mthd()
+    }
+  }
+
+transparent inline def transform[T](expr: T): T = ??? // if we add inline to param, it doesn't crash
+
+trait Generic[+T] { // both covariance and contravariance cause a crash (invariance doesn't)
+  def mthd(): Generic[T] = ??? // has to have a parameter list to crash
+}

tests/pos-macros/i15475a/Macro_1.scala

@@ -0,0 +1,17 @@
+package x
+
+import scala.quoted.*
+
+
+transparent inline def xtransform[T](inline expr:T) = ${
+   X.transform('expr)
+}
+
+object X {
+
+   def transform[T:Type](x: Expr[T])(using Quotes):Expr[T] = {
+      import quotes.reflect.*
+      x
+   }
+
+}

tests/pos-macros/i15475a/Test_2.scala

@@ -0,0 +1,15 @@
+package x
+
+def hello = {
+  xtransform {
+    val a: Seq[Generic[?]] = null
+    a
+      .foreach { to =>
+        to.mthd()
+      }
+  }
+}
+
+trait Generic[+T] {
+  def mthd(): Generic[T] = this
+}