broaden criterion dependency range

This crate builds and tests fine against criterion 0.5.1 or 0.4.0;
while those versions are semver-incompatible, the crate itself uses a
common set of compatible features from criterion.

This adjustment in the explicit dependencies represents that
flexibility.

If criterion 0.5.1 is selected, and that package has a higher MSRV
than 0.72, then the aggregate MSRV will be higher.  But this package
won't be the limiting factor.

Cargo.toml

@@ -33,7 +33,7 @@ rand = "0.8.5"
 regex = "1.10.2"
 hex = "0.4.3"
 rand_chacha = "0.3.1"
-criterion = "0.4.0" # Needed to keep MSRV back at 1.72, newer: "0.5.1"
+criterion = ">=0.4.0, <0.6" # 0.4.0 Needed to keep MSRV back at 1.72, also builds fine with 0.5.1
 flate2 = "1.0.27"