[Broadcom] Upgrade xgs SAI version to 12.3.7.2 (sonic-net#22425)

Why I did it
Upgrade the xgs SAI version to 12.3.7.2 to include the following change:

12.3.7.2: [ECMP] set max ECMP group member count to SDK when configured
Work item tracking
Microsoft ADO (number only): 32483287
How I did it
Upgrade the SAI version in the sai.mk file.

How to verify it
on a 7260 T1, verify nexthop_group number is correct:

admin@bjw-can-7260-12:~$ crm show resources all

Resource Name           Used Count    Available Count
--------------------  ------------  -----------------
ipv4_route                    6475             288437
ipv6_route                    6456              26312
ipv4_nexthop                    24              49102
ipv6_nexthop                    24              49102
ipv4_neighbor                   24               8120
ipv6_neighbor                   24               4060
nexthop_group_member            10              16374
nexthop_group                    3                253
fdb_entry                        0               8191
ipmc_entry                       0               4096
snat_entry                       0               1024
dnat_entry                       0               1024

admin@bjw-can-7260-12:~$ bcmcmd 'bsv'
bsv
BRCM SAI ver: [12.3.6.5], OCP SAI ver: [1.15.0], SDK ver: [sdk-6.5.31-SP10]
drivshell>
admin@bjw-can-7260-12:~$

Author: Gfrom2016

platform/broadcom/sai.mk

@@ -1,4 +1,4 @@
-LIBSAIBCM_XGS_VERSION = 12.3.6.2
+LIBSAIBCM_XGS_VERSION = 12.3.7.2
 LIBSAIBCM_DNX_VERSION = 12.3.2.2
 LIBSAIBCM_XGS_BRANCH_NAME = SAI_12.3.0_GA
 LIBSAIBCM_DNX_BRANCH_NAME = SAI_12.3.0_GA