fix: src/loadgenerator/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DEBIAN12-ZLIB-6008963
- https://snyk.io/vuln/SNYK-DEBIAN12-SHADOW-5879156
- https://snyk.io/vuln/SNYK-DEBIAN12-SQLITE3-2407042
- https://snyk.io/vuln/SNYK-DEBIAN12-SQLITE3-6139924
- https://snyk.io/vuln/SNYK-DEBIAN12-UTILLINUX-2401083

src/loadgenerator/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM python:3.8-slim as base
+FROM python:3.13-slim as base
 
 FROM base as builder