Fix Spellcheck Error in X64/DxePagingAuditTests.c (#140)

## Description

The spellcheck interpreted DxePagingAuditTestsx86.c as containing the
word Testsx due to case sensitivity. Regardless, the header comment had
the incorrect file name. This update fixes the spellcheck issue by
updating the header comment.

- [ ] Impacts functionality?
- [ ] Impacts security?
- [ ] Breaking change?
- [ ] Includes tests?
- [ ] Includes documentation?

## How This Was Tested

N/A - Comment change

## Integration Instructions

N/A

UefiTestingPkg/AuditTests/PagingAudit/UEFI/Dxe/App/AArch64/DxePagingAuditTests.c

@@ -1,4 +1,4 @@
-/** @file -- DxePagingAuditTestsArm64.c
+/** @file -- DxePagingAuditTests.c
     ARM64 implementations for DXE paging audit tests
 
     Copyright (c) Microsoft Corporation.

UefiTestingPkg/AuditTests/PagingAudit/UEFI/Dxe/App/X64/DxePagingAuditTests.c

@@ -1,5 +1,5 @@
-/** @file -- DxePagingAuditTestsx86.c
-    x86 implementations for DXE paging audit tests
+/** @file -- DxePagingAuditTests.c
+    X64 implementations for DXE paging audit tests
 
     Copyright (c) Microsoft Corporation.
     SPDX-License-Identifier: BSD-2-Clause-Patent