Update to Debian Bullseye, musl 1.2.2

```
 amd64/hello-world/hello    | Bin 13336 -> 13256 bytes
 arm32v5/hello-world/hello  | Bin 8948 -> 8948 bytes
 arm32v7/hello-world/hello  | Bin 4848 -> 4848 bytes
 arm64v8/hello-world/hello  | Bin 9136 -> 9136 bytes
 i386/hello-world/hello     | Bin 12984 -> 12924 bytes
 mips64le/hello-world/hello | Bin 7680 -> 7768 bytes
 ppc64le/hello-world/hello  | Bin 66400 -> 66400 bytes
 riscv64/hello-world/hello  | Bin 4976 -> 4976 bytes
 s390x/hello-world/hello    | Bin 9192 -> 9056 bytes
```

Dockerfile.build

@@ -1,5 +1,5 @@
 # explicitly use Debian for maximum cross-architecture compatibility
-FROM debian:buster-slim
+FROM debian:bullseye-slim
 
 RUN set -eux; \
 	apt-get update; \
@@ -36,7 +36,7 @@ RUN set -eux; \
 	rm -rf /var/lib/apt/lists/*
 
 # https://musl.libc.org/releases.html
-ENV MUSL_VERSION 1.1.24
+ENV MUSL_VERSION 1.2.2
 RUN set -eux; \
 	wget -O musl.tgz.asc "https://musl.libc.org/releases/musl-$MUSL_VERSION.tar.gz.asc"; \
 	wget -O musl.tgz "https://musl.libc.org/releases/musl-$MUSL_VERSION.tar.gz"; \