hydra-unstable: fix build, pin libpqxx to 6.4.5

pkgs/development/tools/misc/hydra/common.nix

@@ -1,5 +1,5 @@
 { stdenv, nix, perlPackages, buildEnv
-, makeWrapper, autoconf, automake, libtool, unzip, pkg-config, sqlite, libpqxx
+, makeWrapper, autoconf, automake, libtool, unzip, pkg-config, sqlite, libpqxx_6
 , top-git, mercurial, darcs, subversion, breezy, openssl, bzip2, libxslt
 , perl, postgresql, nukeReferences, git, boehmgc, nlohmann_json
 , docbook_xsl, openssh, gnused, coreutils, findutils, gzip, xz, gnutar
@@ -82,7 +82,7 @@ in stdenv.mkDerivation rec {
   inherit stdenv src version patches;
 
   buildInputs =
-    [ makeWrapper autoconf automake libtool unzip nukeReferences sqlite libpqxx
+    [ makeWrapper autoconf automake libtool unzip nukeReferences sqlite libpqxx_6
       top-git mercurial /*darcs*/ subversion breezy openssl bzip2 libxslt
       perlDeps perl nix
       postgresql # for running the tests