Do not try to benchmark normal test cases

Currently running cargo bench -- --save-baseline master doesn't work,
for the reasons outlined in [1].

Apply the fix in the comment ([2]) to not try to load the normal tests
during benchmarking.

[1]: bheisler/criterion.rs#193
[2]: bheisler/criterion.rs#193 (comment)

Cargo.toml

@@ -13,6 +13,9 @@ crc24 = "0.1.6"
 [dev-dependencies]
 criterion = "0.5"
 
+[lib]
+bench = false
+
 [[bench]]
 name = "fast_vs_fallback"
 harness = false