ci: include some timing information in the git cache download script

In https://gitlab.freedesktop.org/zmike/mesa/-/jobs/46476087 it is unclear
whether this script is where 30+ minutes were lost, or if this ran fine and
the `git clone` afterwards is where the issue was.

Printing these timestamps will help next time something like this happens.

Signed-off-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24452>

.gitlab-ci/download-git-cache.sh

@@ -15,7 +15,7 @@ fi
 
 TMP_DIR=$(mktemp -d)
 
-echo "Downloading archived master..."
+echo "$(date +"%F %T") Downloading archived master..."
 if ! /usr/bin/wget \
 	      -O "$TMP_DIR/$CI_PROJECT_NAME.tar.gz" \
               "https://${S3_HOST}/git-cache/${FDO_UPSTREAM_REPO}/$CI_PROJECT_NAME.tar.gz";
@@ -27,8 +27,10 @@ fi
 set -e
 
 rm -rf "$CI_PROJECT_DIR"
-echo "Extracting tarball into '$CI_PROJECT_DIR'..."
+echo "$(date +"%F %T") Extracting tarball into '$CI_PROJECT_DIR'..."
 mkdir -p "$CI_PROJECT_DIR"
 tar xzf "$TMP_DIR/$CI_PROJECT_NAME.tar.gz" -C "$CI_PROJECT_DIR"
 rm -rf "$TMP_DIR"
 chmod a+w "$CI_PROJECT_DIR"
+
+echo "$(date +"%F %T") Git cache download done"