Digital Signature Hash Algorithms Not Validated in sylabs/sif

syslabs/sif is the Singularity Image Format (SIF) reference implementation. In versions prior to 2.8.1the `github.com/sylabs/sif/v2/pkg/integrity` package did not verify that the hash algorithm(s) used are cryptographically secure when verifying digital signatures. A patch is available in version >= v2.8.1 of the module. Users are encouraged to upgrade. Users unable to upgrade may independently validate that the hash algorithm(s) used for metadata digest(s) and signature hash are cryptographically secure.