[ty] Skip flaky symlink file-watching test (#28702)

`symlink_inside_project` intermittently fails in Linux CI because the
indexed project files unexpectedly include the symlinked `bar/baz.py`
path. Ignore the test temporarily and add a TODO to re-enable it once
symlink file-watching is reliable in CI.

## Test plan

No new tests are added. The existing test remains available to run
explicitly, and the other symlink file-watching tests remain enabled
where supported.

crates/ty/tests/file_watching.rs

@@ -2193,6 +2193,8 @@ mod unix {
     ///   |-- foo.py
     /// ```
     #[test]
+    // TODO: Re-enable once symlink file-watching is reliable in CI.
+    #[ignore = "Flaky symlink file-watching test"]
     fn symlink_inside_project() -> anyhow::Result<()> {
         let mut case = setup(|context: &mut SetupContext| {
             // Set up the symlink target.