docs(metrics): fix test references (#5265)

Signed-off-by: Emmanuel Ferdman <[email protected]>

Author: emmanuel-ferdman

Diff for: docs/core/metrics.md

@@ -430,4 +430,4 @@ You can read standard output and assert whether metrics have been flushed. Here'
     ```
 
 ???+ tip
-    For more elaborate assertions and comparisons, check out [our functional testing for Metrics utility.](https://github.com/aws-powertools/powertools-lambda-python/blob/develop/tests/functional/metrics/test_metrics_cloudwatch_emf.py){target="_blank"}
+    For more elaborate assertions and comparisons, check out [our functional testing for Metrics utility.](https://github.com/aws-powertools/powertools-lambda-python/blob/develop/tests/functional/metrics/required_dependencies/test_metrics_cloudwatch_emf.py){target="_blank"}

Diff for: docs/core/metrics/datadog.md

@@ -257,4 +257,4 @@ You can read standard output and assert whether metrics have been flushed. Here'
     ```
 
 ???+ tip
-    For more elaborate assertions and comparisons, check out [our functional testing for DatadogMetrics utility.](https://github.com/aws-powertools/powertools-lambda-python/blob/develop/tests/functional/metrics/test_metrics_datadog.py){target="_blank"}
+    For more elaborate assertions and comparisons, check out [our functional testing for DatadogMetrics utility.](https://github.com/aws-powertools/powertools-lambda-python/blob/develop/tests/functional/metrics/datadog/test_metrics_datadog.py){target="_blank"}