Bump 3rdparty/Megatron-LM from 844119f to 99f23d2 (#528)

Bumps [3rdparty/Megatron-LM](https://github.com/NVIDIA/Megatron-LM) from
`844119f` to `99f23d2`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/99f23d2f111d12b73b1fbf386c60517101ff8abe"><code>99f23d2</code></a>
Merge branch 'fix-external-dataloader' into 'main'</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/ebfc79b632393b7729e7bc0dff5809b0c453621f"><code>ebfc79b</code></a>
ADLR/megatron-lm!2453 - Fix wrapping of external dataloaders</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/fd69c2f2fb366c20d8e18f875dabc42b2f0dca99"><code>fd69c2f</code></a>
Merge branch 'fix-assert-warning' into 'main'</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/281644543097e9089e0e9b4b264c4a0a91877dca"><code>2816445</code></a>
ADLR/megatron-lm!2443 - Fix assert warning in !2282</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/371feef2b7dd619038bdacb82fe0e195ebad67ee"><code>371feef</code></a>
Merge branch 'trintamaki/small-model-example' into 'main'</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/2aa3522a5fe7aa2dd18561122c40fc8840e3b2f5"><code>2aa3522</code></a>
ADLR/megatron-lm!2432 - Small VLM example</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/215a2eb2c5cad942cd095976539bc74c6ae9d622"><code>215a2eb</code></a>
Merge branch 'xren/cp_llava' into 'main'</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/40fb590e4bb4aa01053f1c09d6d5f58992f8cf53"><code>40fb590</code></a>
ADLR/megatron-lm!2404 - move get_batch_on_this_cp_rank to mcore
utils</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/d4e72c0d33edc0c53aeb624f617eb77cebce6ae9"><code>d4e72c0</code></a>
Merge branch 'dnarayanan/skip_all_gather_first_iteration' into
'main'</li>
<li><a
href="https://github.com/NVIDIA/Megatron-LM/commit/44b6480511f194ccb3943fbf590bc146e6612160"><code>44b6480</code></a>
ADLR/megatron-lm!2414 - Remove all-gather before first iteration to not
sprea...</li>
<li>Additional commits viewable in <a
href="https://github.com/NVIDIA/Megatron-LM/compare/844119f5c856a3037ec7c7f6d6ef7b3518ceee6b...99f23d2f111d12b73b1fbf386c60517101ff8abe">compare
view</a></li>
</ul>
</details>
<br />


Dependabot will resolve any conflicts with this PR as long as you don't
alter it yourself. You can also trigger a rebase manually by commenting
`@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

---

<details>
<summary>Dependabot commands and options</summary>
<br />

You can trigger Dependabot actions by commenting on this PR:
- `@dependabot rebase` will rebase this PR
- `@dependabot recreate` will recreate this PR, overwriting any edits
that have been made to it
- `@dependabot merge` will merge this PR after your CI passes on it
- `@dependabot squash and merge` will squash and merge this PR after
your CI passes on it
- `@dependabot cancel merge` will cancel a previously requested merge
and block automerging
- `@dependabot reopen` will reopen this PR if it is closed
- `@dependabot close` will close this PR and stop Dependabot recreating
it. You can achieve the same result by closing it manually
- `@dependabot show <dependency name> ignore conditions` will show all
of the ignore conditions of the specified dependency
- `@dependabot ignore this major version` will close this PR and stop
Dependabot creating any more for this major version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this minor version` will close this PR and stop
Dependabot creating any more for this minor version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this dependency` will close this PR and stop
Dependabot creating any more for this dependency (unless you reopen the
PR or upgrade to it yourself)


</details>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>