include, tests: Address concerns from -Wsign-compare

After switching to Debian Trixie these surfaced as issues when building
locally.

Change-Id: I92a4d19579257e796aa29be8d4fb79fe92466780
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/tests/dsp/file.cpp b/tests/dsp/file.cpp
index cf5b11d..b8fe67f 100644
--- a/tests/dsp/file.cpp
+++ b/tests/dsp/file.cpp
@@ -555,7 +555,7 @@
     auto rc = encode_pldm_file_df_open_resp(instance_id, &resp_data,
                                             responsePtr, &payload_length);
     EXPECT_EQ(rc, 0);
-    EXPECT_EQ(payload_length, 1); // Completion code only
+    EXPECT_EQ(payload_length, 1ul); // Completion code only
 }
 #endif