i16601 Fix class name in error message

[nizhikov]

No description provided.

[nizhikov]

fixes #16601

Don't like the asInstanceOf

[nizhikov]

Hello @dwijnand - thanks for the review.
I replaced asInstanceOf with match.
Can you, please, advice me - what compiler suppose to do in case type not expected?
Right now I fallback to previous message.

        if (cls.isOneOf(AbstractOrTrait)) {
          srcTp.underlyingClassRef(refinementOK = false) match 
            case tref0: TypeRef => 
              val srcCls = tref0.symbol
              report.error(CantInstantiateAbstractClassOrTrait(srcCls, isTrait = srcCls.is(Trait)), pos)
            case _ => 
              report.error(CantInstantiateAbstractClassOrTrait(cls, isTrait = cls.is(Trait)), pos)
        }

[nizhikov]

@dwijnand Thanks for the review.

All checks passed. Anything else should be done prior merge?