boot/edk2: bump to version edk2-stable202308

For change log since version edk2-stable202305, see:
- https://github.com/tianocore/edk2/releases/tag/edk2-stable202308

The main motivations of this bump are the RISC-V QEMU Virt support
improvements (not yet supported in Buildroot).

Cc: Dick Olsson <hi@senzilla.io>
Cc: Vincent Stehlé <vincent.stehle@arm.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

boot/edk2/edk2.hash

@@ -1,3 +1,3 @@
 # Locally calculated
-sha256  ca55351913e6258ebd8c08106f369ac71073d9cfaa80427fc5f131b06d808940  edk2-edk2-stable202305-br1.tar.gz
+sha256  9389ad20bc75f2a8fa9e7c1b1948ef07481c94e96dec57ae2f9f9be9c754f92c  edk2-edk2-stable202308-br1.tar.gz
 sha256  50ce20c9cfdb0e19ee34fe0a51fc0afe961f743697b068359ab2f862b494df80  License.txt

boot/edk2/edk2.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-EDK2_VERSION = edk2-stable202305
+EDK2_VERSION = edk2-stable202308
 EDK2_SITE = https://github.com/tianocore/edk2
 EDK2_SITE_METHOD = git
 EDK2_LICENSE = BSD-2-Clause-Patent