Update alpine docker image tag

Dockerfile

-FROM rust:alpine3.14
+FROM rust:alpine3.18
 ENV RUSTFLAGS="-C target-feature=-crt-static"
 WORKDIR /usr/src/rebuilderd
 RUN apk add --no-cache musl-dev openssl-dev shared-mime-info sqlite-dev xz-dev zstd-dev
@@ -10,7 +10,7 @@ RUN --mount=type=cache,target=/var/cache/buildkit \
     cp -v /var/cache/buildkit/target/release/rebuilderd \
         /var/cache/buildkit/target/release/rebuildctl /
 
-FROM alpine:3.14
+FROM alpine:3.18
 RUN apk add --no-cache libgcc openssl shared-mime-info sqlite-libs xz zstd-libs
 COPY --from=0 \
     /rebuilderd /rebuildctl \

worker/Dockerfile.alpine

-FROM rust:alpine3.14
+FROM rust:alpine3.18
 ENV RUSTFLAGS="-C target-feature=-crt-static"
 WORKDIR /usr/src/rebuilderd
 RUN apk add --no-cache musl-dev openssl-dev pkgconfig
@@ -9,7 +9,7 @@ RUN --mount=type=cache,target=/var/cache/buildkit \
     cargo build --release --locked -p rebuilderd-worker && \
     cp -v /var/cache/buildkit/alpine/target/release/rebuilderd-worker /
 
-FROM alpine:3.14
+FROM alpine:3.18
 RUN apk add --no-cache libgcc openssl
 COPY --from=0 /rebuilderd-worker /usr/local/bin/
 ENV REBUILDERD_WORKER_BACKEND=alpine=/usr/local/libexec/rebuilderd/rebuilder-alpine.sh