CI: detect failure to run make docomp nicely again

We have a test for our CI which detects if a PR should have run `make docomp`.
But we did not reach it anymore since some changes to `bin/BuildPackages.sh`
which added code to use GAP to extract the name of any given packages, by
letting GAP print it to stdout and grabbing it from there. But in this
particular failure scenario, GAP also printed a warning, which caused
`BuildPackages.sh` to fail. This patch suppresses that warning.

bin/BuildPackages.sh

@@ -194,7 +194,7 @@ run_configure_and_make() {
  then
  if grep Autoconf ./configure > /dev/null
  then
- local PKG_NAME=$($GAP -q -T -A -r <<GAPInput
+ local PKG_NAME=$($GAP -q -T -A -r -M <<GAPInput
 Read("PackageInfo.g");
 Print(GAPInfo.PackageInfoCurrent.PackageName);
 GAPInput