Gate the last path-casing test to the platform it describes

EnqueueMatchesRegardlessOfPathCase asserts two paths differing only in
case are one entry, which the previous commit made true only where the
file system says so. It is the same mistake twice: I fixed the two the
Linux legs reported and did not go looking for the rest, and this one
lives in the project the arm64 leg does not run.

Swept every test project for path casing this time. This was the only one
left; the others touching case are about tool names, environment
variables and extension matching, none of which changed.

Verified by forcing the folding off, building - and checking the build
actually succeeded, which the last two attempts at this did not, so they
were reporting stale binaries - then listing every failing test. All nine
are the RunOn(Windows) ones that real Linux skips, and nothing else moved.

Author: SimonCropp

src/DiffEngine.Tests/InlineQueueTests.cs

@@ -45,9 +45,11 @@ public async Task EnqueueReplacesTheSameCallSite()
     }
 
     /// <summary>
-    /// The same path can reach here with different casing, and it is still one call site.
+    /// The same path can reach here with different casing, and where the file system says those
+    /// are one file it is still one call site.
     /// </summary>
     [Test]
+    [RunOn(TUnit.Core.Enums.OS.Windows)]
     public async Task EnqueueMatchesRegardlessOfPathCase()
     {
         var queue = InlineQueue.Empty
@@ -57,6 +59,21 @@ public async Task EnqueueMatchesRegardlessOfPathCase()
         await Assert.That(queue.Count).IsEqualTo(1);
     }
 
+    /// <summary>
+    /// And where it says they are two files, two call sites. Matching them everywhere gave both
+    /// one entry: the second patch replaced the first, and settling either settled both.
+    /// </summary>
+    [Test]
+    [RunOn(TUnit.Core.Enums.OS.Linux)]
+    public async Task EnqueueKeepsPathCaseApartWhereTheFilesDo()
+    {
+        var queue = InlineQueue.Empty
+            .Enqueue(Patch("Sample.cs"))
+            .Enqueue(Patch("SAMPLE.CS"));
+
+        await Assert.That(queue.Count).IsEqualTo(2);
+    }
+
     [Test]
     public async Task SettleRemoves()
     {