fix(ci): Profiling Tests (Weekly) workflow failing on main

[mvillmow]

Repairs Profiling Tests (Weekly) (run 25620831958, persistent across at least the last two weekly runs).

RC

Tooling/environment. CMake configure failed with:

CMake Error at /usr/local/share/cmake-3.31/Modules/FindPackageHandleStandardArgs.cmake:233 (message):
  Could NOT find GTest (missing: GTEST_LIBRARY GTEST_INCLUDE_DIR
  GTEST_MAIN_LIBRARY)

profiling-weekly.yml installed clang/cmake/ninja but never ran conan install. GTest is supplied via Conan (gtest/1.14.0 in conanfile.py) and required by find_package(GTest REQUIRED) in CMakeLists.txt:115.

Fix

Adopt the same pattern _required.yml uses for every other C++ build job:

• Replace ad-hoc apt-get install block with the canonical ./.github/actions/install-build-deps composite action (installs clang-18, cmake, ninja, AND conan with a detected profile).
• Cache ~/.conan2 keyed on hashFiles('conanfile.py').
• Add a conan install step (Release, cppstd=20) before the CMake configure.
• Pass -DCMAKE_TOOLCHAIN_FILE=build/conan-deps/conan_toolchain.cmake so find_package(GTest REQUIRED) resolves.

Net change: +18 / -14 lines, scoped to .github/workflows/profiling-weekly.yml only.

Test plan

• Trigger via workflow_dispatch after merge and confirm green