smplayer: fix hash after upstream replaced their git tag

Our smplayer package received a normal update with commit
https://github.com/NixOS/nixpkgs/commit/8d99101d35fdfbbff0465dd899334321eee61363 .
After that commit and a corresponding pull request
got created with https://github.com/NixOS/nixpkgs/pull/415020 ,
upstream apparently added a new commit
https://github.com/smplayer-dev/smplayer/commit/b62faa90efb6c6be8e0938a42e70fbfb3916feb6
to their repository, and replaced the git tag (release tag)
https://github.com/smplayer-dev/smplayer/releases/tag/v25.6.0 .
This tag previously pointed to
https://github.com/smplayer-dev/smplayer/commit/4a27de33a4cab71215002f138daab1e3c69ca7ef
for which the old nixpkgs hash is valid.

Due to the invalidation of the old git tag,
we have to adapt our source hash.