docs: Fix @example blocks in gpu_management.md (#1571)

* Fix `@example` blocks in gpu_management.md

* Combine `@example` blocks in gpu_management.md

Author: abhro

docs/src/manual/gpu_management.md

@@ -31,32 +31,32 @@ Automatic Backend Management is done by two simple functions: `cpu_device` and `
 
 * [`cpu_device`](@ref): This is a simple function and just returns a `CPUDevice` object.
 
-   ```@example gpu_management
-   cdev = cpu_device()
-   ```
+  ```@example gpu_management
+  cdev = cpu_device()
 
-   ```@example gpu_management
-   x_cpu = randn(Float32, 3, 2)
-   ```
+  x_cpu = randn(Float32, 3, 2)
+  ```
 
 * [`gpu_device`](@ref): This function performs automatic GPU device selection and returns
-   an object.
-   1. If no GPU is available, it returns a `CPUDevice` object.
-   2. If a LocalPreferences file is present, then the backend specified in the file is used.
-      To set a backend, use `Lux.gpu_backend!(<backend_name>)`. (a) If the trigger package
-      corresponding to the device is not loaded, then a warning is displayed. (b) If no
-      LocalPreferences file is present, then the first working GPU with loaded trigger
-      package is used.
-
-   ```@example gpu_management
-   gdev = gpu_device()
-
-   x_gpu = x_cpu |> gdev
-   ```
-
-   ```@example gpu_management
-   (x_gpu |> cdev) ≈ x_cpu
-   ```
+  an object.
+
+  1. If no GPU is available, it returns a `CPUDevice` object.
+
+  2. If a LocalPreferences file is present, then the backend specified in the file is used.
+     To set a backend, use `Lux.gpu_backend!(<backend_name>)`. (a) If the trigger package
+     corresponding to the device is not loaded, then a warning is displayed. (b) If no
+     LocalPreferences file is present, then the first working GPU with loaded trigger
+     package is used.
+
+  ```@example gpu_management
+  gdev = gpu_device()
+
+  x_gpu = x_cpu |> gdev
+  ```
+
+  ```@example gpu_management
+  (x_gpu |> cdev) ≈ x_cpu
+  ```
 
 ## Manual Backend Management