Skip unavailable nss_wrapper on ppc64le

[yosifkit]

This will fix the current failing builds on ppc64le:

+ apk add --no-cache --virtual .postgresql-rundeps so:libLLVM-15.so so:libc.musl-ppc64le.so.1 so:libcrypto.so.3 so:libedit.so.0 so:libgcc_s.so.1 so:libgssapi_krb5.so.2 so:libicui18n.so.72 so:libicuuc.so.72 so:libldap.so.2 so:libssl.so.3 so:libstdc++.so.6 so:libuuid.so.1 so:libxml2.so.2 so:libxslt.so.1 so:libz.so.1 bash nss_wrapper su-exec tzdata zstd icu-data-full
fetch https://dl-cdn.alpinelinux.org/alpine/v3.17/main/ppc64le/APKINDEX.tar.gz
fetch https://dl-cdn.alpinelinux.org/alpine/v3.17/community/ppc64le/APKINDEX.tar.gz
ERROR: unable to select packages:
  .postgresql-rundeps-20221222.204533:
    masked in: cache
    satisfies: world[.postgresql-rundeps=20221222.204533]
  nss_wrapper (no such package):
    required by: .postgresql-rundeps-20221222.204533[nss_wrapper]

Related to #1018