Format .nix files

This does not include any automation for the release branch, but
is based on the configuration of https://github.com/NixOS/nix/pull/12349

    pre-commit run -a nixfmt-rfc-style

tests/nixos/fetch-git/default.nix

@@ -7,26 +7,27 @@
   ];
 
   /*
-  Test cases
+    Test cases
 
-  Test cases are automatically imported from ./test-cases/{name}
+    Test cases are automatically imported from ./test-cases/{name}
 
-  The following is set up automatically for each test case:
-    - a repo with the {name} is created on the gitea server
-    - a repo with the {name} is created on the client
-    - the client repo is configured to push to the server repo
+    The following is set up automatically for each test case:
+      - a repo with the {name} is created on the gitea server
+      - a repo with the {name} is created on the client
+      - the client repo is configured to push to the server repo
 
-  Python variables:
-    - repo.path: the path to the directory of the client repo
-    - repo.git: the git command with the client repo as the working directory
-    - repo.remote: the url to the server repo
+    Python variables:
+      - repo.path: the path to the directory of the client repo
+      - repo.git: the git command with the client repo as the working directory
+      - repo.remote: the url to the server repo
   */
-  testCases =
-    map
-    (testCaseName: {...}: {
+  testCases = map (
+    testCaseName:
+    { ... }:
+    {
       imports = [ (./test-cases + "/${testCaseName}") ];
       # ensures tests are named like their directories they are defined in
       name = testCaseName;
-    })
-    (lib.attrNames (builtins.readDir ./test-cases));
+    }
+  ) (lib.attrNames (builtins.readDir ./test-cases));
 }