Fix misused glob in BUILD.qt_win.bazel (#1151)

This follows up to my previous commit [1], which aimed to enable us to
use Bazel to build executables with Qt6 dependencies.

Thanks to '--incompatible_disallow_empty_glob', which is going to be
enabled by default from Bazel 8.0, it is clear that an empty list was
set to 'hdrs' despite my intention. Let's fix it (#1150).

There must be no change in the final artifacts.

 [1]: 019911b

PiperOrigin-RevId: 709014821

src/bazel/BUILD.qt_win.bazel

@@ -25,7 +25,9 @@ cc_library(
         ],
     }),
     hdrs = glob([
-        "include",
+        "include/QtCore/*",
+        "include/QtGui/*",
+        "include/QtWidgets/*",
     ]),
     includes = [
         "include",