Fix fmt.Errorf format argument in ParseFullReference

The error path passed an int to fmt.Errorf with %q, which expects a
string. Use the original reference string to avoid a format mismatch.

Signed-off-by: Mikel Olasagasti Uranga <mikel@olasagasti.info>

pkg/cmd/pr/shared/finder.go

@@ -349,7 +349,7 @@ func ParseFullReference(s string) (ghrepo.Interface, int, error) {
 
 	number, err := strconv.Atoi(m[3])
 	if err != nil {
-		return nil, 0, fmt.Errorf("invalid reference: %q", number)
+		return nil, 0, fmt.Errorf("invalid reference: %q", s)
 	}
 
 	owner := m[1]