Workbench: Different branch for AWS CLI v2.

Until https://github.com/aws/aws-cli/issues/9234 is resolved, use the
branch which allows a newer ruamel-yaml-clib which can be installed with
Python 3.13. Once Python 3.13 is supported, revert this commit.

workbench/Dockerfile

@@ -255,7 +255,7 @@ RUN export PIP_CONSTRAINT=/tmp/constraint.txt && \
     unset PIP_CONSTRAINT && \
     pipx install chalice && \
     pipx install curator-opensearch && \
-    CFLAGS="-Wno-error=incompatible-pointer-types" pipx install https://github.com/aws/aws-cli/archive/refs/heads/v2.zip && \
+    CFLAGS="-Wno-error=incompatible-pointer-types" pipx install https://github.com/aws/aws-cli/archive/refs/heads/dependabot/pip/v2/ruamel-yaml-clib-0.2.12.zip && \
     rm -rf /tmp/* /var/tmp/* ~/.cache/*
 ENV COREPACK_HOME=/usr/local/share/corepack
 # hadolint ignore=DL3016