C#: fix compilation error in IR

Author: rdmarsh2

csharp/ql/src/semmle/code/csharp/ir/internal/TempVariableTag.qll

@@ -8,7 +8,8 @@ newtype TTempVariableTag =
   ForeachEnumTempVar() or
   LockedVarTemp() or
   LockWasTakenTemp() or
-  EllipsisTempVar()
+  EllipsisTempVar() or
+  ThisTempVar()
 
 string getTempVariableTagId(TTempVariableTag tag) {
   tag = ConditionValueTempVar() and result = "CondVal"
@@ -26,4 +27,6 @@ string getTempVariableTagId(TTempVariableTag tag) {
   tag = LockWasTakenTemp() and result = "LockWasTakenTemp"
   or
   tag = EllipsisTempVar() and result = "Ellipsis"
+  or
+  tag = ThisTempVar() and result = "This"
 }