Fix #6373: Consider synthetic inlined methods as inline methods

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -803,7 +803,7 @@ object SymDenotations {
     def isSkolem: Boolean = name == nme.SKOLEM
 
     def isInlineMethod(implicit ctx: Context): Boolean =
-      is(InlineMethod, butNot = AccessorOrSynthetic) &&
+      is(InlineMethod, butNot = Accessor) &&
       name != nme.unapply  // unapply methods do not count as inline methods
                            // we need an inline flag on them only do that
                            // reduceProjection gets access to their rhs

tests/pos/i6373.scala

@@ -0,0 +1,13 @@
+object Test {
+  class Test  {
+    class Context(val t: Boolean)
+
+    type Contextual[T] = given Context => T
+
+    inline def f(): Contextual[Boolean] = the[Context].t
+
+    implied ctx for Context = new Context(true)
+
+    f()
+  }
+}