Kea with CB configured on PostgreSQL 15 cannot prepare statement

Newer PostgreSQL servers seem to be more picky about how prepared statements are formatted. Kea fails to start because of a missing space between a placeholder and the WHERE keyword.

ERROR [kea-dhcp6.dhcp6] DHCP6_INIT_FAIL failed to initialize Kea server: configuration error using file '/etc/kea-dhcp6.conf': during update from config backend database: unable to prepare PostgreSQL statement:  name: UPDATE_SUBNET6, reason: ERROR:  trailing junk after parameter at or near "$33W"
LINE 1: ...threshold = cast($32 as float),  cache_max_age =  $33WHERE s...

This is also visible in multiple unit tests in PgSqlConfigBackendDHCPv6Test.

[ RUN      ] PgSqlConfigBackendDHCPv6Test.getType
*** ERROR: unable to open database. The test
*** environment is broken and must be fixed before
*** the tests will run correctly.
*** The reason for the problem is described in the
*** accompanying exception output.
unknown file: Failure
C++ exception with description "unable to prepare PostgreSQL statement:  name: UPDATE_SUBNET6, reason: ERROR:  trailing junk after parameter at or near "$33W"
LINE 1: ...threshold = cast($32 as float),  cache_max_age =  $33WHERE s...
                                                             ^
, text: UPDATE dhcp6_subnet SET  subnet_id = $1,  subnet_prefix = $2,  client_class = $3,  interface = $4,  modification_ts = $5,  preferred_lifetime = $6,  min_preferred_lifetime = $7,  max_preferred_lifetime = $8,  rapid_commit = $9,  rebind_timer = $10,  relay = $11,  renew_timer = $12,  require_client_classes = $13,  reservations_global = $14,  shared_network_name = $15,  user_context = cast($16 as json),  valid_lifetime = $17,  min_valid_lifetime = $18,  max_valid_lifetime = $19,  calculate_tee_times = $20,  t1_percent = cast($21 as float),  t2_percent = cast($22 as float),  interface_id = $23,  ddns_send_updates = $24,  ddns_override_no_update = $25,  ddns_override_client_update = $26,  ddns_replace_client_name = $27,  ddns_generated_prefix = $28,  ddns_qualifying_suffix = $29,  reservations_in_subnet = $30,  reservations_out_of_pool = $31,  cache_threshold = cast($32 as float),  cache_max_age =  $33WHERE subnet_id = $34 OR subnet_prefix = $35" thrown in SetUp().
[  FAILED  ] PgSqlConfigBackendDHCPv6Test.getType (249 ms)

Adding the space makes the unit tests pass.

Affected PostgreSQL versions: 15.0, 15.1.

It works properly on PostgreSQL 14.6.