Do not add dummy RHS to abstract inline methods (#16510)

Fixes #16508

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/PickleQuotes.scala

@@ -113,7 +113,7 @@ class PickleQuotes extends MacroTransform {
             case _ =>
               val (contents, tptWithHoles) = makeHoles(tpt)
               PickleQuotes(quotes, tptWithHoles, contents, tpt.tpe, true)
-        case tree: DefDef if tree.symbol.is(Macro) || tree.symbol.isInlineMethod =>
+        case tree: DefDef if !tree.rhs.isEmpty && tree.symbol.isInlineMethod =>
           // Shrink size of the tree. The methods have already been inlined.
           // TODO move to FirstTransform to trigger even without quotes
           cpy.DefDef(tree)(rhs = defaultValue(tree.rhs.tpe))