update maint/check_licenses

maint/check_licenses needs to be updated, "fuchsia-cprng" is no longer a dependency since !479 (merged) and arti depends on 3 crates for which there is "no license"

• tinystr which license is ok for arti (not detected because it's Apache-2.0/MIT, and the tool used consider only Apache-2.0 OR MIT to be valid)
• ring which license is "ISC-style", so probably ok but someone should probably read it entirely to verify?
• webpki, same as for ring but less text to read

Maybe this script should be used in CI to make sure it's kept up to date and no non-compatible license gets added by mistake?