participant-integration-api: Increase the migration connection timeout. (#7558)

250ms is a bit low for CI when our database might be overloaded.

5 seconds seems like a decent balance between a quick response and
being sympathetic to slow/overloaded machines.

CHANGELOG_BEGIN
CHANGELOG_END

ledger/participant-integration-api/src/main/scala/platform/store/FlywayMigrations.scala

@@ -63,7 +63,7 @@ private[platform] class FlywayMigrations(jdbcUrl: String)(implicit loggingContex
       jdbcUrl = jdbcUrl,
       minimumIdle = 2,
       maxPoolSize = 2,
-      connectionTimeout = 250.millis,
+      connectionTimeout = 5.seconds,
       metrics = None,
     )
 }