fix!: Ensure that MeasurementIndexShardId is non-negative (#1863)

BREAKING CHANGE: This is updating an existing Liquibase changeset, and will therefore require manual adjustments wherever it has been rolled out. This should only have rolled out to Halo test environments.

Closes #1862

src/main/resources/kingdom/spanner/shard-measurements-by-continuation-token.sql

@@ -21,7 +21,7 @@ START BATCH DDL;
 
 ALTER TABLE Measurements
 ADD COLUMN MeasurementIndexShardId INT64 NOT NULL AS (
-  MOD(FARM_FINGERPRINT(CAST(MeasurementId AS STRING)), 64)
+  ABS(MOD(FARM_FINGERPRINT(CAST(MeasurementId AS STRING)), 64))
 ) STORED;
 
 DROP INDEX MeasurementsByContinuationToken;