jammy-amd64-tf-a-build: Use explicit Rust version; update to 1.85.0

Last commit (9efacf0ce5bd969f7a103bfdd2602797926e6499) fixed the
version to 1.82.0 and addressed
https://linaro.atlassian.net/browse/TFC-677

Add support for a later toolchain, namely, 1.85.0.

Change-Id: I8965a1c55f99d28ed31a1b97d28e141d96823b1a
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 da1ff34..65b24e2 100644
--- a/jammy-amd64-tf-a-build/Dockerfile
+++ b/jammy-amd64-tf-a-build/Dockerfile
@@ -109,7 +109,7 @@
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
-        sh -s -- --default-toolchain 1.82.0 -y
+        sh -s -- --default-toolchain 1.85.0 -y
 RUN set -ex ;\
     cargo install 'tokei@12.1.*' ;\
     cargo install cargo-binutils ;\