Fix #8126 (#8712)

This is a temporary fix that will be reworked in a follow up commit
that aims to eliminate the tfExplicit flag from the compiler. The
complete and proper fix was considered too risky for inclusion just
before our 0.19 release.

compiler/ast.nim

@@ -506,6 +506,7 @@ type
     tfGenericTypeParam
     tfImplicitTypeParam
     tfInferrableStatic
+    tfConceptMatchedTypeSym
     tfExplicit        # for typedescs, marks types explicitly prefixed with the
                       # `type` operator (e.g. type int)
     tfWildcard        # consider a proc like foo[T, I](x: Type[T, I])