schemaparse: do not capture annotation strings

src/preserves/schemaparse.nim

@@ -287,7 +287,7 @@ const parser = peg("Schema", p: ParseState):
   Value <- Preserves.Value:
     discard
 
-  Annotation <- '@' * (Preserves.String | Preserves.Record) * S
+  Annotation <- '@' * ('"' * *Preserves.char * '"' | Preserves.Record) * S
 
   S <- *{ ' ', '\t', '\r', '\n' }