CI doesn't catch doc build error.

[anlowee]

Problem description

The current CI doesn't catch the syntax errors in the doc. For example:

/home/velox/velox/docs/develop/connectors.rst:163: WARNING: malformed hyperlink target. [docutils]
writing output... [ 11%] develop/connectors
/home/velox/velox/docs/develop/connectors.rst:134: WARNING: undefined label: 'clps3authproviderbase' [ref.ref]

This is an obvious syntax error but the CI can still pass with it.

System information

Velox System Info v0.0.2
Commit: 17c1f23
CMake Version: 3.28.3
System: Linux-4.15.0-210-generic
Arch: x86_64
C++ Compiler: /usr/bin/c++
C++ Compiler Version: 11.4.0
C Compiler: /usr/bin/cc
C Compiler Version: 11.4.0
CMake Prefix Path: /usr/local;/usr;/;/usr/local/lib/python3.10/dist-packages/cmake/data;/usr/local;/usr/X11R6;/usr/pkg;/opt

CMake log