containers: add myself to the maintainers of the tests

Seems like the right thing to do.

nixos/tests/containers-bridge.nix

···
 import ./make-test.nix ({ pkgs, ...} : {
   name = "containers-bridge";
   meta = with pkgs.stdenv.lib.maintainers; {
-    maintainers = [ aristid aszlig eelco chaoflow ];
+    maintainers = [ aristid aszlig eelco chaoflow kampfschlaefer ];
   };
 
   machine =

nixos/tests/containers-extra_veth.nix

···
 import ./make-test.nix ({ pkgs, ...} : {
   name = "containers-bridge";
   meta = with pkgs.stdenv.lib.maintainers; {
-    maintainers = [ aristid aszlig eelco chaoflow ];
+    maintainers = [ kampfschlaefer ];
   };
 
   machine =

nixos/tests/containers-imperative.nix

···
 import ./make-test.nix ({ pkgs, ...} : {
   name = "containers-imperative";
   meta = with pkgs.stdenv.lib.maintainers; {
-    maintainers = [ aristid aszlig eelco chaoflow ];
+    maintainers = [ aristid aszlig eelco chaoflow kampfschlaefer ];
   };
 
   machine =

nixos/tests/containers-ipv4.nix

···
 import ./make-test.nix ({ pkgs, ...} : {
   name = "containers-ipv4";
   meta = with pkgs.stdenv.lib.maintainers; {
-    maintainers = [ aristid aszlig eelco chaoflow ];
+    maintainers = [ aristid aszlig eelco chaoflow kampfschlaefer ];
   };
 
   machine =

nixos/tests/containers-ipv6.nix

···
 import ./make-test.nix ({ pkgs, ...} : {
   name = "containers-ipv6";
   meta = with pkgs.stdenv.lib.maintainers; {
-    maintainers = [ aristid aszlig eelco chaoflow ];
+    maintainers = [ aristid aszlig eelco chaoflow kampfschlaefer ];
   };
 
   machine =