nix: format test fixtures via nix fmt

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Ia9c1e9b0a8cd9c6d834f153609baa5426a6a6964

tests/string_interp.nix

@@ -3,17 +3,20 @@ let
   name = "world";
   x = 42;
   bool_val = true;
-in
-  {
-    # Simple interpolation
-    greeting = "Hello ${name}!";
+in {
+  # Simple interpolation
+  greeting = "Hello ${name}!";
 
-    # Multiple interpolations
-    multi = "x is ${x} and name is ${name}";
+  # Multiple interpolations
+  multi = "x is ${x} and name is ${name}";
 
-    # Nested expression
-    nested = "Result: ${if bool_val then "yes" else "no"}";
+  # Nested expression
+  nested = "Result: ${
+    if bool_val
+    then "yes"
+    else "no"
+  }";
 
-    # Just a string (no interpolation)
-    plain = "plain text";
-  }
+  # Just a string (no interpolation)
+  plain = "plain text";
+}