chore(deps): update docker.io/library/alpine docker tag to v3.18 (#18)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Dockerfile

@@ -14,7 +14,7 @@ RUN cargo chef cook --release --recipe-path recipe.json
 COPY . .
 RUN cargo build --release --bin http-cache
 
-FROM docker.io/library/alpine:3.17 AS runtime
+FROM docker.io/library/alpine:3.18 AS runtime
 WORKDIR app
 COPY --from=builder /app/target/release/http-cache /usr/local/bin/http-cache
 ENTRYPOINT ["http-cache"]