freezes php docker version

Dockerfile

@@ -34,7 +34,7 @@ RUN mv /opt/rustdeps/target/$(uname -m)-unknown-linux-musl/release/librustdeps.a
 # | |         | |       | |     __/ |
 # |_|         |_|       |_|    |___/
 
-FROM php:7.3-fpm-alpine as phpspy-builder
+FROM php:7.3-fpm-alpine3.13 as phpspy-builder
 RUN apk add --update alpine-sdk
 RUN git clone https://github.com/pyroscope-io/phpspy.git && cd phpspy && git checkout 024461fbba5130a1dc7fd4f0b5a458424cf50b3a
 RUN cd phpspy && make CFLAGS="-DUSE_DIRECT"