Keep the Date spy and only scope the colon check to the filename

The earlier switch to jest fake timers froze time for the rest of the
suite and broke the test on every platform. The Date constructor spy
already pins the timestamp correctly, as the original Windows failure
showed the right pinned value. The only real problem was that the colon
check looked at the full path, which on Windows starts with a drive
letter like D: that legitimately contains a colon. Restore the spy and
keep the assertion scoped to the basename.

Author: LeSingh1

libraries/rush-lib/src/api/test/ChangeFile.test.ts

@@ -20,10 +20,11 @@ describe(ChangeFile.name, () => {
       .mockReturnValue({ branch: 'my-branch' } as any);
 
     // Pin the clock to 2017-05-01 20:20:30 UTC so the timestamp is deterministic.
-    // Use Jest fake timers so new Date() is intercepted at the engine level, which is
-    // more reliable than spying on the Date constructor (the spy approach is fragile on
-    // Windows with Node.js v24 because the V8 Date fast-path can bypass the spy).
-    jest.useFakeTimers().setSystemTime(new Date('2017-05-01T20:20:30.000Z'));
+    const fixedDate: Date = new Date('2017-05-01T20:20:30.000Z');
+    const dateSpy: jest.SpyInstance = jest
+      .spyOn(global, 'Date')
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      .mockImplementation(() => fixedDate as any);
 
     try {
       const changeFile: ChangeFile = new ChangeFile(
@@ -46,7 +47,7 @@ describe(ChangeFile.name, () => {
       // includes a drive letter (e.g. "D:\...") which legitimately contains a colon.
       expect(filename).not.toContain(':');
     } finally {
-      jest.useRealTimers();
+      dateSpy.mockRestore();
       getGitInfoSpy.mockRestore();
     }
   });