ci: run clippy on features separately to find issues (open-telemetry#2866)

Co-authored-by: Cijo Thomas <[email protected]>

Author: bantonsson

src/lib.rs

@@ -1,4 +1,10 @@
 pub mod logs_asserter;
+#[cfg(any(
+    feature = "hyper-client",
+    feature = "reqwest-client",
+    feature = "reqwest-blocking-client",
+    feature = "tonic-client"
+))]
 pub mod metric_helpers;
 pub mod test_utils;
 pub mod trace_asserter;