.loading
Various code was using fomantic `loading` class which I think got broken a while ago and rendered only a full circle. Fix those to use `is-loading`. Before: <img width="295" alt="Screenshot 2024-03-19 at 22 56 26" src="https://github.com/go-gitea/gitea/assets/115237/dbe83395-5db4-4868-90bc-3613866a35f0"> After: <img width="60" alt="Screenshot 2024-03-19 at 22 54 35" src="https://github.com/go-gitea/gitea/assets/115237/8ac19b7e-035a-4c6d-850b-53a234ef69c2"> <img width="294" alt="Screenshot 2024-03-19 at 22 54 56" src="https://github.com/go-gitea/gitea/assets/115237/34e819d7-25f7-43a1-9d48-4a68dcd2b6ad"> <img width="320" alt="Screenshot 2024-03-19 at 22 55 16" src="https://github.com/go-gitea/gitea/assets/115237/05127544-47ff-4e18-9fd8-c84e44c374f8"> <img width="153" alt="Screenshot 2024-03-19 at 23 01 43" src="https://github.com/go-gitea/gitea/assets/115237/a33248c6-b11d-40ff-82d8-f5a3d85b55aa"> <img width="1300" alt="Screenshot 2024-03-19 at 23 56 25" src="https://github.com/go-gitea/gitea/assets/115237/562ca876-b5d5-4295-961e-9d2cdab31ab0"> <img width="136" alt="Screenshot 2024-03-20 at 00 00 38" src="https://github.com/go-gitea/gitea/assets/115237/44838ac4-67f3-4fec-a8e3-978cc5dbdb72"> (cherry picked from commit d6fed9ab88b13e124c5e59ceac5b21a3af52ad24)
