Explicitly install libdb-dev when building Python runtimes (#1582)

Required so that the Python `dbm.ndbm` stdlib module will be built, now
that `libdb-dev` is no longer in the Heroku-24 build image:
heroku/base-images#303

(These headers are only needed when the Python runtimes are being
compiled. The run image still has the necessary runtime library
counterparts.)

GUS-W-15159536.

builds/Dockerfile

@@ -9,6 +9,7 @@ USER root
 
 RUN apt-get update --error-on=any \
     && apt-get install -y --no-install-recommends \
+      libdb-dev \
       libreadline-dev \
       libsqlite3-dev \
     && rm -rf /var/lib/apt/lists/*