do less renovate pinning - starting out with docker images

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

plugins/scaffolder-backend-module-rails/Rails.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3@sha256:24af4f0bf0af61d04a5ead4f43e7ad468a1b2ff05844d7780555a13a78615ced
+FROM ruby:3.3
 
 RUN apt-get update -qq && \
     apt-get install -y nodejs postgresql-client git && \

plugins/scaffolder-backend/scripts/Cookiecutter.dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.18@sha256:11e21d7b981a59554b3f822c49f6e9f57b6068bb74f49c4cd5cc4c663c7e5160
+FROM alpine:3.18
 
 RUN apk add --update \
 	git \
@@ -8,4 +8,4 @@ RUN apk add --update \
 	g++ && \
 	pip install cookiecutter && \
 	apk del g++ py-pip python-dev && \
-	rm -rf /var/cache/apk/* 
+	rm -rf /var/cache/apk/*