Bump nushell version from 0.111.0 to 0.112.2 and Alpine to 3.23.4

Exercism's policy is to prefer pinned versions.
Using the same hash across all runners allows us to store and reuse the same image, rather than needing to store a per-runner base image. This helps cut down on storage costs.

Author: IsaacG

Dockerfile

@@ -1,10 +1,10 @@
-FROM alpine:3.22
+FROM alpine:3.23.4@sha256:5b10f432ef3da1b8d4c7eb6c487f2f5a8f096bc91145e68878dd4a5019afde11
+ARG VERSION=0.112.2
 
 RUN apk add --no-cache jq curl && \
-    curl -Lo nu.tgz https://github.com/nushell/nushell/releases/download/0.111.0/nu-0.111.0-x86_64-unknown-linux-musl.tar.gz && \
-    gunzip nu.tgz && \
-    tar xvf nu.tar  && \
-    mv nu-0.111.0-x86_64-unknown-linux-musl/nu /usr/bin 
+    curl -L https://github.com/nushell/nushell/releases/download/${VERSION}/nu-${VERSION}-x86_64-unknown-linux-musl.tar.gz \
+    | tar xzOT <(echo nu-${VERSION}-x86_64-unknown-linux-musl/nu) > /usr/bin/nu && \
+    chmod 755 /usr/bin/nu
 
 
 WORKDIR /opt/test-runner