Fix typo from unit to uint (#121884)

Fix typo from `unit` to `uint` in comment.

Author: prozolic

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/LengthBucketsFrozenDictionary.AlternateLookup.cs

@@ -49,7 +49,7 @@ private ref readonly TValue GetValueRefOrNullRefCoreAlternate(ReadOnlySpan<char>
                     }
                     else
                     {
-                        // -1 is used to indicate a null, when it's casted to unit it becomes > keys.Length
+                        // -1 is used to indicate a null, when it's casted to uint it becomes > keys.Length
                         break;
                     }
                 }

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/LengthBucketsFrozenDictionary.cs

@@ -81,7 +81,7 @@ private protected override ref readonly TValue GetValueRefOrNullRefCore(string k
                         }
                         else
                         {
-                            // -1 is used to indicate a null, when it's casted to unit it becomes > keys.Length
+                            // -1 is used to indicate a null, when it's casted to uint it becomes > keys.Length
                             break;
                         }
                     }
@@ -100,7 +100,7 @@ private protected override ref readonly TValue GetValueRefOrNullRefCore(string k
                         }
                         else
                         {
-                            // -1 is used to indicate a null, when it's casted to unit it becomes > keys.Length
+                            // -1 is used to indicate a null, when it's casted to uint it becomes > keys.Length
                             break;
                         }
                     }

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/LengthBucketsFrozenSet.AlternateLookup.cs

@@ -48,7 +48,7 @@ private int FindItemIndexAlternate(ReadOnlySpan<char> item)
                     }
                     else
                     {
-                        // -1 is used to indicate a null, when it's casted to unit it becomes > items.Length
+                        // -1 is used to indicate a null, when it's casted to uint it becomes > items.Length
                         break;
                     }
                 }