GHA: return error code from curl if install fails

Until now, a failure to install MantisBT was detected by the CI builds
during the subsequent phase "Post-installation steps" as it generally
impossible to complete it if the database is not setup correctly.

With this change, if the MantisBT installer exits with an HTTP error
code (>= 400), curl will fail with an exit code 22. The --fail-with-body
option allows displaying the installer's output.

That allows GitHub Actions to catch the error when it occurs, during the
"Install MantisBT" phase.

Fixes 0036916