Alan Zimmerman authored Dec 21, 2021 and Marge Bot committed Dec 22, 2021

A declaration such as

    infixr ++++

is supplied with an implicit fixity of 9 in the parser, but uses
an invalid SrcSpan to capture this. Use of this span triggers a panic.

Fix the problem by not recording an exact print annotation for the
non-existent fixity source.

Closes #20846