A Small Mistake in lockfree_queue.md

There is a minor typo in the Pop Operation section of the iceoryx/doc/design/lockfree_queue.md document, where the state of the queue after a pop operation is incorrectly illustrated. Specifically, the positions of x and y are swapped.

## Current Document:
### Pop Operation

Pop reads the value at the index of head and returns it if the cycle matches Heads cycle and a CAS to increase head by 1 succeeds.

```
[ (c,?), (c,y), (c,x), (c-1,?) ] H=(c,1) T=(c,3)
```

pop returns y

```
[ (c,?), (c,x), (c,y), (c-1,?) ] H=(c,2) T=(c,3)
```

## Corrected Document:

Pop reads the value at the index of head and returns it if the cycle matches Heads cycle and a CAS to increase head by 1 succeeds.

```
[ (c,?), (c,x), (c,y), (c-1,?) ] H=(c,1) T=(c,3)
```

pop returns y

```
[ (c,?), (c,x), (c,y), (c-1,?) ] H=(c,2) T=(c,3)
```

Thank you.

Open iceoryx/doc/design/lockfree_queue.md and go to the Pop Operation section. Compare the two queue-state diagrams with the described pop result, correct the swapped positions of x and y in the first diagram, and confirm both diagrams consistently show pop returning y.

Written by the indexing model from the issue text.