fix nits

src/Avalonia.Controls/TextBox.cs

@@ -212,10 +212,10 @@ namespace Avalonia.Controls
             {
                 if (!_ignoreTextChanges)
                 {
-                    var carretIndex = CaretIndex;
+                    var caretIndex = CaretIndex;
                     SelectionStart = CoerceCaretIndex(SelectionStart, value?.Length ?? 0);
                     SelectionEnd = CoerceCaretIndex(SelectionEnd, value?.Length ?? 0);
-                    CaretIndex = CoerceCaretIndex(carretIndex, value?.Length ?? 0);
+                    CaretIndex = CoerceCaretIndex(caretIndex, value?.Length ?? 0);
 
                     if (SetAndRaise(TextProperty, ref _text, value) && !_isUndoingRedoing)
                     {

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -322,7 +322,7 @@ namespace Avalonia.Controls.UnitTests
         }
 
         [Fact]
-        public void SelectionEnd_Dont_Cause_Exception()
+        public void SelectionEnd_Doesnt_Cause_Exception()
         {
             using (UnitTestApplication.Start(Services))
             {
@@ -344,7 +344,7 @@ namespace Avalonia.Controls.UnitTests
         }
 
         [Fact]
-        public void SelectionStart_Dont_Cause_Exception()
+        public void SelectionStart_Doesnt_Cause_Exception()
         {
             using (UnitTestApplication.Start(Services))
             {