vmTools: download debs from snapshot URLs

The deb files we want are no longer available in the Debian mirrors,
so we need to download them from the snapshots we download the package
lists from.

This makes it possible to build the os-prober NixOS test again.

(cherry picked from commit 64bfa05)

pkgs/build-support/vm/default.nix

@@ -1018,7 +1018,7 @@ rec {
         url = "https://snapshot.debian.org/archive/debian/20221126T084953Z/dists/buster/main/binary-i386/Packages.xz";
         hash = "sha256-n9JquhtZgxw3qr9BX0MQoY3ZTIHN0dit+iru3DC31UY=";
       };
-      urlPrefix = "mirror://debian";
+      urlPrefix = "https://snapshot.debian.org/archive/debian/20221126T084953Z";
       packages = commonDebianPackages;
     };
 
@@ -1029,7 +1029,7 @@ rec {
         url = "https://snapshot.debian.org/archive/debian/20221126T084953Z/dists/buster/main/binary-amd64/Packages.xz";
         hash = "sha256-YukIIB3u87jgp9oudwklsxyKVKjSL618wFgDSXiFmjU=";
       };
-      urlPrefix = "mirror://debian";
+      urlPrefix = "https://snapshot.debian.org/archive/debian/20221126T084953Z";
       packages = commonDebianPackages;
     };
 
@@ -1040,7 +1040,7 @@ rec {
         url = "https://snapshot.debian.org/archive/debian/20230131T034648Z/dists/bullseye/main/binary-i386/Packages.xz";
         hash = "sha256-z9eG7RlvelEnZAaeCfIO+XxTZVL3d+zTA7ShU43l/pw=";
       };
-      urlPrefix = "mirror://debian";
+      urlPrefix = "https://snapshot.debian.org/archive/debian/20230131T034648Z";
       packages = commonDebianPackages;
     };
 
@@ -1051,7 +1051,7 @@ rec {
         url = "https://snapshot.debian.org/archive/debian/20230131T034648Z/dists/bullseye/main/binary-amd64/Packages.xz";
         hash = "sha256-mz0eCWdn6uWt40OxsSPheHzEnMeLE52yR/vpb48/VF0=";
       };
-      urlPrefix = "mirror://debian";
+      urlPrefix = "https://snapshot.debian.org/archive/debian/20230131T034648Z";
       packages = commonDebianPackages;
     };
   };