chore(deps): update postgis/postgis docker tag to v18

Author: renovate[bot]

docker/postgres/Dockerfile

@@ -1,10 +1,10 @@
-FROM postgis/postgis:17-3.6-alpine AS pgvector-builder
+FROM postgis/postgis:18-3.6-alpine AS pgvector-builder
 RUN apk add --no-cache git build-base clang19 llvm19
 RUN git clone --branch v0.8.1 https://github.com/pgvector/pgvector.git /tmp/pgvector
 RUN make -C /tmp/pgvector -j "$(nproc)"
 RUN make -C /tmp/pgvector -j "$(nproc)" install
 
-FROM postgis/postgis:17-3.6-alpine
+FROM postgis/postgis:18-3.6-alpine
 RUN apk add --no-cache postgresql17-plpython3
 COPY --from=pgvector-builder /usr/local/lib/postgresql/bitcode/vector.index.bc /usr/local/lib/postgresql/bitcode/vector.index.bc
 COPY --from=pgvector-builder /usr/local/lib/postgresql/vector.so /usr/local/lib/postgresql/vector.so