util-docker: Update systemc docker image to use 22.04

Updates the Dockerfile, and therefore the Docker image, to use Ubuntu
22.04 instead of Ubuntu 20.04.

Change-Id: I0969205159d47ece9b0b6c0452ce0f3420f32e4c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/69317
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
diff --git a/util/dockerfiles/systemc-2.3.3/Dockerfile b/util/dockerfiles/systemc-2.3.3/Dockerfile
index 0653a86..ac94666 100644
--- a/util/dockerfiles/systemc-2.3.3/Dockerfile
+++ b/util/dockerfiles/systemc-2.3.3/Dockerfile
@@ -24,7 +24,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-FROM ubuntu:20.04
+FROM ubuntu:22.04
 
 ENV DEBIAN_FRONTEND=noninteractive
 RUN apt -y update && apt -y upgrade && \