Update Alpine image to version 3.16 (#1)

Why:
We're using this action for a while (3 years) and it is still being built based on a outdated alpine version. A docker scan showed that it has a critical vulnerability that it's fixed on later versions.
Screenshot 2022-06-15 at 18 05 51
More info: https://security.snyk.io/vuln/SNYK-ALPINE310-APKTOOLS-1534688

Doing the same scan when using alpine:3.16 showed no known vulnerabilities.
Screenshot 2022-06-15 at 18 07 46

Also, since the action has no changes for a while, it's best if we keep doing security updates while we still use it.

This addresses the issue by:
- Update docker container alpine:3.10 to alpine:3.16 (latest ATOW)

Author: nunoapfernandes

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.10
+FROM alpine:3.16
 
 RUN apk add -U bash git dos2unix