chore: Update container version to g538dba3

We have switched to git sha1 tagging since v49. For details, see:
rust-vmm/rust-vmm-container#121.

Signed-off-by: Ruoqing He <[email protected]>

Author: RuoqingHe

.buildkite/autogenerate_pipeline.py

@@ -60,7 +60,7 @@
 
 # This represents the version of the rust-vmm-container used
 # for running the tests.
-CONTAINER_VERSION = "v48"
+CONTAINER_VERSION = "g538dba3"
 # The suffix suggests that the dev image with `v{N}-riscv` tag is not to be
 # confused with real `riscv64` image (it's actually a `x86_64` image with
 # `qemu-system-riscv64` installed), since AWS yet has `riscv64` machines