build(deps): bump flash-attn from 2.6.1 to 2.6.3

Bumps [flash-attn](https://github.com/Dao-AILab/flash-attention) from 2.6.1 to 2.6.3.
- [Release notes](https://github.com/Dao-AILab/flash-attention/releases)
- [Commits](Dao-AILab/flash-attention@v2.6.1...v2.6.3)

---
updated-dependencies:
- dependency-name: flash-attn
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

pyproject.toml

@@ -64,7 +64,7 @@ dev = [
 flash_attn = [
   # it's easier to install flash-attn from wheel rather than like this as extra
   # "https://github.com/Dao-AILab/flash-attention/releases/download/v2.5.6/flash_attn-2.5.6+cu118torch2.0cxx11abiFALSE-cp311-cp311-linux_x86_64.whl",
-  "flash-attn==2.6.1",
+  "flash-attn==2.6.3",
   "packaging",  # FIXME: temporary, until https://github.com/Dao-AILab/flash-attention/pull/937 is released
   "ninja"
 ]