chore(deps): update alpine docker tag to v3.21

Author: renovate[bot]

Dockerfile

@@ -5,7 +5,7 @@ RUN go mod download
 COPY . .
 RUN CGO_ENABLED=0 go build -o loli ./cmd/loli/main.go
 
-FROM alpine:3.18
+FROM alpine:3.21
 WORKDIR /app
 COPY --from=builder /app/loli ./
 ENTRYPOINT [ "/app/loli" ]