jammy-amd64-tf-a-build: Use explicit Rust version; update to 1.88.0

Last commit (3b16008ad2fe380133ee2d4a10fb0018fed952ca) fixed the
version to 1.85.0. See commit for more information.

Add support for a later toolchain, namely, 1.88.0

Change-Id: I0d269c619fbf6756c4c3101a102481a13a678056
Signed-off-by: Tomás González <tomasagustin.gonzalezorlando@arm.com>
diff --git a/jammy-amd64-tf-a-build/Dockerfile b/jammy-amd64-tf-a-build/Dockerfile
index 63e28f2..853f344 100644
--- a/jammy-amd64-tf-a-build/Dockerfile
+++ b/jammy-amd64-tf-a-build/Dockerfile
@@ -110,7 +110,7 @@
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
-        sh -s -- --default-toolchain 1.85.0 -y
+        sh -s -- --default-toolchain 1.88.0 -y
 RUN set -ex ;\
     cargo install --locked 'tokei@12.1.*' ;\
     cargo install --locked cargo-binutils ;\