Deb: On upgrades, stop both mysqld and mariadbd for backwards compat

debian/mariadb-server-10.5.postrm

@@ -18,9 +18,12 @@ stop_server() {
     # Return immediately if there are no mysql processes running
     # as there is no point in trying to shutdown in that case.
     if ! pgrep -x mariadbd > /dev/null; then return; fi
+    # Compatibility with versions that ran 'mysqld'
+    if ! pgrep -x mysqld > /dev/null; then return; fi
 
     set +e
     invoke-rc.d mariadb stop
+    invoke-rc.d mysql stop # Backwards compatibility
     errno=$?
     set -e
 

debian/mariadb-server-10.5.preinst

@@ -31,9 +31,12 @@ stop_server() {
     # Return immediately if there are no mysql processes running
     # as there is no point in trying to shutdown in that case.
     if ! pgrep -x --ns $$ mariadbd > /dev/null; then return; fi
+    # Compatibility with versions that ran 'mysqld'
+    if ! pgrep -x --ns $$ mysqld > /dev/null; then return; fi
 
     set +e
     invoke-rc.d mariadb stop
+    invoke-rc.d mysql stop # Backwards compatibility
     errno=$?
     set -e