build(telemetry): add src/ include path for ValidationTracker test

The telemetry test module compiles ValidationTracker.cpp (from src/xrpld/)
into xrpl_tests and includes <xrpld/telemetry/ValidationTracker.h>. The
single-binary test scheme dropped the src/ include directory that the old
per-module target carried, breaking the build. Restore it on the telemetry
branch of the test CMakeLists.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/tests/libxrpl/CMakeLists.txt

@@ -62,7 +62,9 @@ if(telemetry)
         PRIVATE opentelemetry-cpp::opentelemetry-cpp
     )
     # ValidationTracker lives in src/xrpld/ (not libxrpl), so we compile its
-    # implementation directly into the test binary.
+    # implementation directly into the test binary and put src/ on the include
+    # path so its tests can reach <xrpld/telemetry/...> headers.
+    target_include_directories(xrpl_tests PRIVATE ${CMAKE_SOURCE_DIR}/src)
     target_sources(
         xrpl_tests
         PRIVATE