fix: positioning of comments on unmodified lines

If there's a comment that needs to be added to a Github PR review,
and it's on an unmodified line, and pint can't find a modified line to put the comment on,
then just put the comment on the first changed line of the diff.

internal/reporter/github.go

@@ -289,7 +289,13 @@ func reportToGitHubComment(headCommit string, rep Report) *github.PullRequestCom
 			msgPrefix,
 			rep.Problem.Text,
 		)),
-		Line: github.Int(reportLine),
+	}
+
+	if reportLine < 0 {
+		// If we couldn't find a nearby line to attach the comment to, put it on the first line of the diff
+		c.Position = github.Int(1)
+	} else {
+		c.Line = github.Int(reportLine)
 	}
 
 	return &c