New height estimation (proposed in gitextensions#6605 (comment) )

Don't know if it solves something...

GitUI/Editor/BlameAuthorMargin.cs

@@ -1,6 +1,8 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Drawing;
 using System.Linq;
+using System.Windows.Forms;
 using GitExtUtils.GitUI;
 using ICSharpCode.TextEditor;
 using Microsoft.VisualStudio.Threading;
@@ -18,10 +20,19 @@ public class BlameAuthorMargin : AbstractMargin
 
         public BlameAuthorMargin(TextArea textArea) : base(textArea)
         {
-            _lineHeight = textArea.Font.Height + 1;
+            _lineHeight = GetFontHeight(textArea.Font);
             _backgroundColor = ((SolidBrush)SystemBrushes.Window).Color;
         }
 
+        private static int GetFontHeight(Font font)
+        {
+            var max = Math.Max(
+                TextRenderer.MeasureText("_", font).Height,
+                (int)Math.Ceiling(font.GetHeight()));
+
+            return max + 1;
+        }
+
         public void SetAvatars(List<JoinableTask<Image>> avatars)
         {
             _avatars = avatars.Select(a => ThreadHelper.JoinableTaskFactory.Run(async () => await a)).ToList();