fix: a not caseSesitive bone should lock the lower value

The idea of _caseINSensitive_ bones is that the upper/lower case
does not matter and `"Test"`, `"test"`, and `"TEST"` are equivalent.

If you now have a unique contstraint `UniqueLockMethod.SameValue`,
it is still possible to create the three entries.

---

Alternatively, we could of course also introduce `UniqueLockMethod.EqualValue`,
which controls this even more precisely.

src/viur/core/bones/base.py

@@ -1045,6 +1045,7 @@ def keyHash(key):
                 return f"K-{keyHash(value)}"
             raise NotImplementedError(f"Type {type(value)} can't be safely used in an uniquePropertyIndex")
 
+        logging.debug(f"_hashValueForUniquePropertyIndex: {value=}")
         if not value and not self.unique.lockEmpty:
             return []  # We are zero/empty string and these should not be locked
         if not self.multiple:

src/viur/core/bones/string.py

@@ -351,6 +351,9 @@ def getUniquePropertyIndexValues(self, skel: "SkeletonInstance", name: str) -> l
             # Not yet implemented as it's unclear if we should keep each language distinct or not
             raise NotImplementedError()
 
+        if not self.caseSensitive and (val := skel[name]) is not None:
+            return self._hashValueForUniquePropertyIndex(val.lower())
+
         return super().getUniquePropertyIndexValues(skel, name)
 
     def refresh(self, skel: "SkeletonInstance", bone_name: str) -> None: