title: Flutter FLCharts Grid not rendering correctly
body: <p>I am showing a chart in my Flutter App using <a href="https://pub.dev/packages/fl_chart" rel="nofollow noreferrer">fl_chart</a> library.
  I am trying to show spots with an y value of either 1, 2, or 3 and I want to draw a horizontal line on the chart on the values 1, 2 and 3.</p>
  <p>Here is my code:</p>
  <pre><code>class MyChart extends StatelessWidget {
    final List&lt;ScatterSpot&gt; spots;
  
    const MyChart({
      Key? key,
      required this.spots,
    }) : super(key: key);
  
    @override
    Widget build(BuildContext context) {
      return ScatterChart(
        ScatterChartData(
          minX: 1,
          maxX: 5,
          minY: 1,
          maxY: 3,
          scatterSpots: spots,
          gridData: FlGridData(
            show: true,
            drawHorizontalLine: true,
            drawVerticalLine: false,
            getDrawingHorizontalLine: (value) {
              return FlLine(
                color: Colors.grey.shade300,
                strokeWidth: 1,
              );
            },
            horizontalInterval: 1,
          ),
          borderData: FlBorderData(
            show: false,
          ),
          titlesData: FlTitlesData(
            leftTitles: SideTitles(
              showTitles: true,
              getTitles: (value) =&gt; value.toString(),
              interval: 1,
            ),
            rightTitles: SideTitles(
              showTitles: false,
            ),
            topTitles: SideTitles(
              showTitles: false,
            ),
            bottomTitles: SideTitles(
              showTitles: false,
            ),
          ),
        ),
      );
    }
  }
  </code></pre>
  <p>So, as you can see, I have defined a minY Value of 1 and a maxY Value of 3. I am drawing a horizontal line with an Interval of 1. The Titles on the y-axis are shown correctly for 1, 2 and 3, but the line is only drawn for the value 2, not for the values 1 and 3. How can I fix this?</p>