[Test][E2E] Stabilize Db2 upsert timestamp comparison

[DanielLeens]

What

• order both timestamp queries by C_INT in JdbcDb2UpsertIT
• keep the before/after timestamp comparison aligned to the same logical rows

Why

JdbcDb2UpsertIT currently compares two query result lists without an ORDER BY. When Db2 returns rows in a different physical order between runs, the assertion can compare timestamps from different rows and fail with microsecond-level mismatches unrelated to the actual upsert behavior.

Validation

• ./mvnw spotless:apply -Dskip.ui=true
• attempted real E2E validation with:
  ./mvnw -B -T 1 verify -DfailIfNoTests=false -DskipUT=true -DskipIT=false -Dlicense.skipAddThirdParty=true -Dskip.ui=true --no-snapshot-updates -pl :connector-jdbc-e2e-part-1 -am -Pci -Dit.test="JdbcDb2UpsertIT#testDb2UpsertE2e"
• local Docker Desktop blocked this E2E before the assertion path: Db2Container timed out waiting for log output matching .*Setup has completed\..* after Db2 finished instance/database creation, so the local run did not reach the updated assertion
• no existing artifacts were intentionally reused; frontend execution in seatunnel-engine-ui was skipped by -Dskip.ui=true during the Maven run