Bump ubuntu from a2bbdf7 to e6173d4 in /images/toolbox (#25)

Bumps ubuntu from `a2bbdf7` to `e6173d4`.

---
updated-dependencies:
- dependency-name: ubuntu
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

images/toolbox/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM ubuntu:22.04@sha256:a2bbdf79d03f6d4171bbd6ebb4782f6229375951987d3427ec3d9373f9841cd7
+FROM ubuntu:22.04@sha256:e6173d4dc55e76b87c4af8db8821b1feae4146dd47341e4d431118c7dd060a74
 
 LABEL maintainer="Antrea <projectantrea-dev@googlegroups.com>"
 LABEL description="A Docker image with useful tools (for networking) based on Ubuntu"