docker: Do not pin the ca-certs pkg version

Hadolint advises to pin a version, but in this specific case isn't
very useful because:
- We always want the latest version for the ca-certificates package
- It has a date-based versioning so we couldn't use the common `=~`
  selector for patch updates. It mostly breaks every time the Alpine
  repository releases a new version because they don't keep the previous one.

Dockerfile

@@ -5,7 +5,8 @@ RUN apk --no-cache add git=~2
 RUN CGO_ENABLED=0 go install -a -trimpath -ldflags "-s -w -X go.k6.io/k6/lib/consts.VersionDetails=$(date -u +"%FT%T%z")/$(git describe --tags --always --long --dirty)"
 
 FROM alpine:3.17
-RUN apk add --no-cache ca-certificates=~20220614 && \
+# hadolint ignore=DL3018
+RUN apk add --no-cache ca-certificates && \
     adduser -D -u 12345 -g 12345 k6
 COPY --from=builder /go/bin/k6 /usr/bin/k6