Upgrade xgs SAI version to 8.4.50.0 (#20136)

Why I did it
Upgrade xgs SAI version to 8.4.50.0 with the following fixes.

8.4.47.0: SAI - OCP SAI 8.4 - [3.5->4.3->8.4] After warmboot to 8.4, MSFT is observing Egress drops on Lossless queues
8.4.48.0: SAI - OTHER - [TH2/TH] Warm reboot from SAI 4.3.5 to SAI 8.4 SONiC image fails
8.4.49.0: SAI - OTHER - [TH2/TH] Warm reboot from SAI 4.3.5 to SAI 8.4 SONiC image fails
8.4.50.0: [CS00012361544] Backport SONIC-93974 to 8.4. Description: MSFT Prod Issue - TD2 device is sending massive PFC
Work item tracking
Microsoft ADO (number only): 29318497
How I did it
Update xgs SAI version to 8.4.50.0 in sai.mk file.

platform/broadcom/sai.mk

@@ -1,4 +1,4 @@
-LIBSAIBCM_XGS_VERSION = 8.4.46.0
+LIBSAIBCM_XGS_VERSION = 8.4.50.0
 LIBSAIBCM_DNX_VERSION = 9.2.12.1
 LIBSAIBCM_XGS_BRANCH_NAME = SAI_8.4.0_GA
 LIBSAIBCM_DNX_BRANCH_NAME = SAI_9.2.0.3