[internal] Fix AWS CLI breaking due to Python 2 usage (pantsbuild#12364)

# Delete this line to force CI to run the JVM tests.
[ci skip-jvm-tests]

build-support/bin/install_aws_cli_for_ci.sh

@@ -17,7 +17,6 @@ fi
 
 AWS_CLI_BIN="${AWS_CLI_ROOT}/bin/aws"
 
-# We first check if AWS CLI is already installed thanks to Travis's cache.
 if [[ ! -x "${AWS_CLI_BIN}" ]]; then
 
   TMPDIR=$(mktemp -d)
@@ -26,7 +25,9 @@ if [[ ! -x "${AWS_CLI_BIN}" ]]; then
 
   curl --fail "https://s3.amazonaws.com/aws-cli/awscli-bundle.zip" -o "awscli-bundle.zip"
   unzip awscli-bundle.zip
-  ./awscli-bundle/install --install-dir "${AWS_CLI_ROOT}"
+  # NB: We must run this with python3 because it defaults to `python`, which refers to Python 2 in Linux GitHub
+  # Actions CI job and is no longer supported.
+  python3 ./awscli-bundle/install --install-dir "${AWS_CLI_ROOT}"
 
   popd