.pytool/CISettings.py: Add subhook submodule

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4389

Add submodule for https://github.com/Zeex/subhook

This submodule is required to hook internal functions
when using gmock.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Michael Kubacki <mikuback@linux.microsoft.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Signed-off-by: Chris Johnson <chris.n.johnson@intel.com>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Oliver Smith-Denny <osde@linux.microsoft.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

.pytool/CISettings.py

@@ -193,6 +193,8 @@ class Settings(CiBuildSettingsManager, UpdateSettingsManager, SetupSettingsManag
             "BaseTools/Source/C/BrotliCompress/brotli", False))
         rs.append(RequiredSubmodule(
             "RedfishPkg/Library/JsonLib/jansson", False))
+        rs.append(RequiredSubmodule(
+            "UnitTestFrameworkPkg/Library/SubhookLib/subhook", False))
         return rs
 
     def GetName(self):