gh-36726: CI Linux: Replace use of pkill
    
Follow-up after:
- #36670

This is working well, for example see https://github.com/mkoeppe/sage/ac
tions/runs/6874334523/job/18695809308#step:11:5345, making it possible
to obtain the image of the hanging build - https://github.com/mkoeppe/sa
ge/actions/runs/6874334523/job/18695809308#step:15:25

However, `pkill` is not present on many of our `-minimal` configurations
(which test our documented minimal build prerequisites). For example
`debian-sid-minimal`, as seen in https://github.com/mkoeppe/sage/actions
/runs/6874334523/job/18695811066#step:11:2262, rendering the mechanism
ineffective there. (Neither are `ps` and `killall`.)

Examples:
- `docker run -it ghcr.io/sagemath/sage/sage-debian-bookworm-minimal-
with-system-packages:dev bash -c "command -v pkill" `
- `docker run -it ghcr.io/sagemath/sage/sage-fedora-38-minimal-with-
system-packages:dev bash -c "command -v pkill"`
- whereas `docker run -it ghcr.io/sagemath/sage/sage-fedora-38-standard-
with-system-packages:dev bash -c "command -v pkill" ` -->
`/usr/bin/pkill`.

We replace `pkill` by more primitive means.

Test run (with timeout set to ~11 minutes for testing purposes): https:/
/github.com/mkoeppe/sage/actions/runs/6883232154/job/18723359505#step:15
:25

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URL: #36726
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Nathan Dunfield, William Stein

Author: Release Manager

.github/workflows/docker.yml

@@ -229,8 +229,17 @@ jobs:
           df -h
         if: inputs.free_disk_space
       - name: Configure and build Sage distribution within a Docker container
+        # The first command below is a self-destruct sequence,
+        # which preempts the GitHub Actions 6-hour job cancellation.
+        #
+        # Using "docker exec", we enter the temporary containers used by
+        # "docker build" and kill the "make" processes of the Sage distribution.
+        #
+        # The arcane "find" command is a replacement for "pkill make",
+        # which we use because pkill is not installed in the "minimal" package
+        # configuration on many platforms.
         run: |
-          (sleep ${{ inputs.timeout }}; for id in $(docker ps -q); do docker exec $id pkill make; done) &
+          (sleep ${{ inputs.timeout }}; for id in $(docker ps -q); do docker exec $id find /proc -maxdepth 2 -name cmdline -exec bash -c "grep -l [m][a][k][e] {} | cut -d/ -f3 | xargs --no-run-if-empty kill" \;; done) &
           set -o pipefail; EXTRA_DOCKER_BUILD_ARGS="--build-arg NUMPROC=4 --build-arg USE_MAKEFLAGS=\"-k V=0 SAGE_NUM_THREADS=3\"" tox -e $TOX_ENV -- $TARGETS 2>&1 | sed "/^configure: notice:/s|^|::warning file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;/^configure: warning:/s|^|::warning file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;/^configure: error:/s|^|::error file=artifacts/$LOGS_ARTIFACT_NAME/config.log::|;"
       - name: Copy logs from the Docker image or build container
         run: |