Fix build error and warning with latest version of core

[emersonknapp]

After ros2/rclcpp#1442 - RCLCPP_DEBUG no longer accepts std::string, so we need to update those places to pass const char *.

(side note there was a build warning for the other string format - and I didn't want to have a PR with warnings)

[codecov]

Codecov Report

Merging #192 (ef625d3) into master (bf375a5) will decrease coverage by 5.28%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #192       +/-   ##
===========================================
- Coverage   34.62%   29.34%    -5.29%     
===========================================
  Files        3012       42     -2970     
  Lines      144506     1847   -142659     
  Branches    91701      918    -90783     
===========================================
- Hits        50042      542    -49500     
+ Misses       8464      445     -8019     
+ Partials    86000      860    -85140     

Flag	Coverage Δ
unittests	29.34% <ø> (-5.29%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...etrics_collector/test_linux_memory_measurement.cpp
...llector/src/system_metrics_collector/utilities.cpp
...trics_collector/test_metrics_message_publisher.cpp
...m_metrics_collector/test_linux_cpu_measurement.cpp
...r/test/system_metrics_collector/test_utilities.cpp
...or/src/topic_statistics_collector/dummy_talker.cpp
...lector/test_linux_process_cpu_measurement_node.cpp
...or/src/topic_statistics_collector/dummy_talker.cpp
...ctor/src/system_metrics_collector/example_main.cpp
...ollector/linux_process_memory_measurement_node.cpp
... and 3020 more

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