CI: upgrade Ubuntu to 24.04 (#524)

GitHubActions' runner image for 'ubuntu-latest' is still running
old LTS 22.04, but we can instead use the 'container:' attribute
to use a docker image in order to use the new Ubuntu LTS 24.04.

This is the most sensible move especially considering that we
have changed CI recently to run on new NodeJS 18.x by default
(Ubuntu 22.04's default NodeJS version is much older than v18).

NOTE: MongoDB service start had to be reworked in this commit to
make it still work in this new distro version.

.github/workflows/integrate.yaml

@@ -12,19 +12,20 @@ on:
 jobs:
   ci_to_main:
     runs-on: ubuntu-latest
+    container:
+      image: 'ubuntu:24.04'
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/setup-node@v1
-        with:
-          node-version: 18.x
+
       - name: Update apt and install required packages
         run: |
-          sudo apt update
-          sudo apt install --yes --no-install-recommends curl
-          sudo apt-get install --yes gnupg
+          apt update --yes
+          apt install --yes sudo
+          sudo apt install --yes --no-install-recommends npm
 
-      - name: Import the public key used by the package management system
+      - name: Import MongoDB's public key for the package management system
         run: |
+          sudo apt install --yes --no-install-recommends curl gnupg
           sudo rm -f /etc/ssl/certs/ca-bundle.crt
           sudo apt reinstall --yes ca-certificates
           sudo update-ca-certificates
@@ -40,9 +41,7 @@ jobs:
       - name: Check Mongo version
         run: mongod --version
       - name: Start MongoDB
-        run: sudo service mongod start
-      - name: Verify that MongoDB has started successfully
-        run: sudo service mongod status
+        run: sudo nohup mongod --quiet --config /etc/mongod.conf &
 
       - name: Create database
         run: |