doxygen.cmake: add working directory when installing

[ahoarau]

This PR fixes a missing working dir on the doc installation script.

To reproduce:
CMakeLists.txt

cmake_minimum_required(VERSION 3.22)

set(PROJECT_NAME jrl-cmakemodules-find-package-test-v1)
set(PROJECT_DESCRIPTION "A project description")
set(PROJECT_URL http://jrl-cmakemodules.readthedocs.io)

include(FetchContent)
FetchContent_Declare(
	jrl-cmakemodules
	GIT_REPOSITORY https://github.com/jrl-umi3218/jrl-cmakemodules.git
)
FetchContent_MakeAvailable(jrl-cmakemodules)

include("${jrl-cmakemodules_SOURCE_DIR}/base.cmake")

project(${PROJECT_NAME} VERSION 1.0.0 LANGUAGES CXX)

cmake -B build -DCMAKE_INSTALL_PREFIX=./install
cmake --build build

Before:

CMake Error at build/cmake_install.cmake:70 (file):
  file INSTALL cannot find "/jrl/build/doc/doxygen-html": No
  such file or directory.

After

-- Configuring "jrl-cmakemodules-find-package-test-v1" (http://jrl-cmakemodules.readthedocs.io)
fatal: not a git repository (or any of the parent directories): .git
-- Failed to find latex/dvips/gs, will use MathJax backend.
-- Create files for AMENT (ROS 2)
-- Configuring done (1.0s)
-- Generating done (0.0s)
-- Build files have been written to: /jrl/build
-- Install configuration: "Debug"
-- Up-to-date: /jrl/install/include/jrl/cmakemodules/find/package/test/v1/config.hh
-- Up-to-date: /jrl/install/include/jrl/cmakemodules/find/package/test/v1/deprecated.hh
-- Up-to-date: /jrl/install/include/jrl/cmakemodules/find/package/test/v1/warning.hh
[1/1] Generating Doxygen documentation
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/doxygen.css
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/graph_legend.md5
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/index.html
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/doxygen_crawl.html
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/jrl-cmakemodules-find-package-test-v1.doxytag
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/doxygen.svg
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/tabs.css
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/graph_legend.png
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/codefolding.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/navtree.css
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/search
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/search/searchdata.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/search/search.css
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/search/search.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/navtree.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/graph_legend.html
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/clipboard.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/navtreeindex0.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/menudata.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/menu.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/navtreedata.js
-- Installing: /jrl/install/share/doc/jrl-cmakemodules-find-package-test-v1/doxygen-html/cookie.js
-- Installing: /jrl/install/lib/pkgconfig/jrl-cmakemodules-find-package-test-v1.pc
-- Installing: /jrl/install/share/ament_index/resource_index/packages/jrl-cmakemodules-find-package-test-v1
-- Installing: /jrl/install/share/jrl-cmakemodules-find-package-test-v1/hook/ament_prefix_path.dsv
-- Installing: /jrl/install/share/jrl-cmakemodules-find-package-test-v1/hook/python_path.dsv