Bump debian in /images/prow-tests (#522)

Bumps debian from bullseye-20240904-slim to bullseye-20240926-slim.

---
updated-dependencies:
- dependency-name: debian
  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/prow-tests/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM debian:bullseye-20240904-slim AS base
+FROM debian:bullseye-20240926-slim AS base
 
 # Pinned versions of stuff we pull in
 ARG TARGETARCH