build: Deny clippy::absolute_paths

Removal of absolute paths is currently in progress. To avoid regressing
those changes add a clippy deny at the workspace level and at the crate
level override with #[expect(clippy::absolute_paths)]

See: #7670

Signed-off-by: Rob Bradford <rbradford@meta.com>

serial_buffer/src/lib.rs

@@ -116,6 +116,8 @@ impl Write for SerialBuffer {
 }
 
 #[cfg(test)]
+// TODO: Trim qualified paths in these tests, then drop this expectation.
+#[expect(clippy::absolute_paths)]
 mod tests {
     use std::io::Write;
     use std::sync::atomic::{AtomicBool, Ordering};