devstack: Add signed-by to MongoDB 8.0 apt source

The MongoDB 8.0 apt repository configuration for Ubuntu 24.04 downloads
the GPG key into /usr/share/keyrings/mongodb-server-8.0.gpg but the deb
source line does not reference it via signed-by. On standard Ubuntu
24.04 systems, apt treats unsigned repositories as a hard error, causing
stack.sh to fail with exit code 100.

Add signed-by=/usr/share/keyrings/mongodb-server-8.0.gpg to the deb
line in both devstack/plugin.sh and tools/test-setup.sh, matching the
pattern already used for Debian 12/13 in test-setup.sh.

Closes-Bug: #2155845
Change-Id: I89a6fa87c4156aff1896aedc67080d637df62fae
Signed-off-by: Martin André <m.andre@redhat.com>

devstack/plugin.sh

@@ -165,7 +165,7 @@ function configure_mongodb {
             curl -fsSL https://pgp.mongodb.com/server-8.0.asc | \
                 sudo gpg -o /usr/share/keyrings/mongodb-server-8.0.gpg \
                 --dearmor
-            echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu noble/mongodb-org/8.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-8.0.list
+            echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-8.0.gpg ] https://repo.mongodb.org/apt/ubuntu noble/mongodb-org/8.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-8.0.list
             sudo apt update
             install_package mongodb-org
             restart_service mongod

tools/test-setup.sh

@@ -41,7 +41,7 @@ if [[ $ubuntu_version == '24.04' ]]; then
     curl -fsSL https://pgp.mongodb.com/server-8.0.asc | \
         sudo gpg -o /usr/share/keyrings/mongodb-server-8.0.gpg \
         --dearmor
-    echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu noble/mongodb-org/8.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-8.0.list
+    echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-8.0.gpg ] https://repo.mongodb.org/apt/ubuntu noble/mongodb-org/8.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-8.0.list
     sudo apt update
     sudo apt install -y mongodb-org
     sudo systemctl restart mongod