Bump python from 3.9.6-slim to 3.9.7-slim

Bumps python from 3.9.6-slim to 3.9.7-slim.

---
updated-dependencies:
- dependency-name: python
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Dockerfile

@@ -63,7 +63,7 @@ RUN ./build_bess.sh && \
     cp -a protobuf /protobuf
 
 # Stage bess: creates the runtime image of BESS
-FROM python:3.9.6-slim AS bess
+FROM python:3.9.7-slim AS bess
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
         gcc \