Some target properties for SOURCE file sets are read-only.

Target properties SOURCE_SETS and INTERFACE_SOURCE_SETS must be read-only.

Source/cmTarget.cxx

@@ -2126,6 +2126,8 @@ bool IsSettableProperty(cmMakefile* context, cmTarget* target,
     { "MANUALLY_ADDED_DEPENDENCIES", { ROC::All } },
     { "NAME", { ROC::All } },
     { "SOURCES", { ROC::Imported } },
+    { "SOURCE_SETS", { ROC::All } },
+    { "INTERFACE_SOURCE_SETS", { ROC::All } },
     { "SYMBOLIC", { ROC::All } },
     { "TYPE", { ROC::All } },
     { "ALIAS_GLOBAL", { ROC::All, cmPolicies::CMP0160 } },