ci(telemetry): state -Dtelemetry=ON instead of relying on the default

Both the CMake option and the Conan recipe default telemetry on, so the
build worked, but this workflow exists to exercise telemetry and should not
depend on a default it does not control. If that default ever flipped, the
binary would build cleanly and then every span and metric assertion would
fail for a reason no log names.

Stated explicitly, the failure mode inverts: CMakeLists.txt does
find_package(opentelemetry-cpp CONFIG REQUIRED) under this option, so a
dependency graph without it fails at configure time with a clear message.
The shared build-deps action is left alone deliberately — forcing the Conan
option there would change every other workflow that uses it.

.github/workflows/telemetry-validation.yml

@@ -156,6 +156,13 @@ jobs:
           build_type: Release
           log_verbosity: verbose
 
+      # telemetry is passed explicitly even though the CMake option and the
+      # Conan recipe both default it on. The whole point of this workflow is to
+      # exercise telemetry, so it should not silently depend on a default it
+      # does not control: if that default ever flips, every span and metric
+      # assertion would fail for a reason no log names. Stated here, a build
+      # without the dependency fails loudly instead, because CMakeLists.txt
+      # does find_package(opentelemetry-cpp CONFIG REQUIRED) under this option.
       - name: Configure CMake
         working-directory: ${{ env.BUILD_DIR }}
         run: |
@@ -163,6 +170,7 @@ jobs:
               -G Ninja \
               -DCMAKE_TOOLCHAIN_FILE:FILEPATH=build/generators/conan_toolchain.cmake \
               -DCMAKE_BUILD_TYPE=Release \
+              -Dtelemetry=ON \
               ..
 
       - name: Build xrpld