Add variadic version of hashFiles

[Bigpet]

fixes #324

I don't know any Go, so double check this.

No idea if this needs some file dedup or if the hashes match the GitHub Actions version, this is just to make sure the same *.yaml code doesn't fail in act while it works in the GH Actions runner

[cplee]

looks great!

[CODY-RAY]

@Bigpet it seems to break when there is a . in the file name

DEBU[0015] Evaluating 'hashFiles('**/package-lock['json']')' instead of 'hashFiles('**/package-lock.json')' ERRO[0015] Unable to interpolate string '${{ hashFiles('**/package-lock.json') }}' - [(anonymous): Line 1:29 Unexpected identifier (and 2 more errors)]