Runtime: Fix swift_getAssociatedTypeWitnessRelativeSlowImpl for MetadataOrPack change

[aschwaighofer]

rdar://106702956

[aschwaighofer]

@swift-ci smoke test

[aschwaighofer]

This fixed a compile error when building in this config: #64361

stdlib/public/runtime/Metadata.cpp:6264:17: error: no matching function for call to 'swift_getTypeByMangledName'                                     
  auto result = swift_getTypeByMangledName(                                                                                                                                                                                                         
                ^~~~~~~~~~~~~~~~~~~~~~~~~~                                                                                                                                                                                                          
stdlib/public/runtime/../CompatibilityOverride/../runtime/Private.h:474:31: note: candidate function not viable: no known conversion from '(lambda at stdlib/public/runtime/Metadata.cpp:6266:7)' to 'SubstGenericParameterFn' (aka 'function<const void *(unsigned int, unsigned int)>') for 4th argument 
TypeLookupErrorOr<TypeInfo> swift_getTypeByMangledName(                                                                                                                                                                                           
                              ^                                                                                                                                                                                                                     
1 error generated.