Fix tidy-check when VCPKG is used

[Noorts]

Problem

Hey team!

The tidy-check job's extension build can fail because the required dependencies are not retrieved by VCPKG. This problem is described by #223.

Changes

I've copied the Setup vcpkg step from the _extension_distribution.yml workflow into the _extension_code_quality.yml workflow. Thus, VCPKG is now installed prior to the extension build.

Furthermore, I've updated the tidy-check Makefile target to include VCPKG in the build process. For that I've taken inspiration from the Makefile's debug target.

Result

Using these changes my tidy-check now successfully builds the extension (including its dependencies).

Before: https://github.com/Noorts/PDXearch/actions/runs/21448678175/job/61771370390

# Before
CMake Warning at CMakeLists.txt:1341 (message):
  Extension 'pdxearch' has a vcpkg.json, but build was not run with VCPKG.
  If build fails, check out VCPKG build instructions in
  'duckdb/extension/README.md' or try manually installing the dependencies in
  /home/runner/work/PDXearch/PDXearch/vcpkg.json


-- Found OpenMP_C: -fopenmp (found version "4.5")
-- Found OpenMP_CXX: -fopenmp (found version "4.5")
-- Found OpenMP: TRUE (found version "4.5")
CMake Error at /home/runner/work/PDXearch/PDXearch/CMakeLists.txt:23 (find_package):
  By not providing "FindEigen3.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "Eigen3", but
  CMake did not find one.

After: https://github.com/Noorts/PDXearch/actions/runs/21448728200/job/61771541738.

Remaining Concerns

I've included USE_MERGED_VCPKG_MANIFEST, but I'm not familiar with the feature and haven't tested it. It would be nice to confirm that the approach is correct, or to change it as necessary.