Bump extern/AMReX-Hydro from 99d6acd to 756c76a (#1555)

Bumps [extern/AMReX-Hydro](https://github.com/AMReX-Fluids/AMReX-Hydro)
from `99d6acd` to `756c76a`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/AMReX-Fluids/AMReX-Hydro/commit/756c76ad6719fde5209ef4bf3b77bd4c1169a44e"><code>756c76a</code></a>
Getters for debugging (<a
href="https://redirect.github.com/AMReX-Fluids/AMReX-Hydro/issues/169">#169</a>)</li>
<li><a
href="https://github.com/AMReX-Fluids/AMReX-Hydro/commit/c90e2c8b17be110faa4ec7cb2e370a3a65e68e3b"><code>c90e2c8</code></a>
make y state consistent with x state wrt limiting before imposing bcs
(<a
href="https://redirect.github.com/AMReX-Fluids/AMReX-Hydro/issues/168">#168</a>)</li>
<li><a
href="https://github.com/AMReX-Fluids/AMReX-Hydro/commit/5998256abd3dd6094efb32cd3cb0b56da23516d7"><code>5998256</code></a>
Fix some issues (<a
href="https://redirect.github.com/AMReX-Fluids/AMReX-Hydro/issues/167">#167</a>)</li>
<li><a
href="https://github.com/AMReX-Fluids/AMReX-Hydro/commit/03773849c48c0329963dbd88516a32906390ebc6"><code>0377384</code></a>
Update Doxygen (<a
href="https://redirect.github.com/AMReX-Fluids/AMReX-Hydro/issues/166">#166</a>)</li>
<li>See full diff in <a
href="https://github.com/AMReX-Fluids/AMReX-Hydro/compare/99d6acd584e92aea5556f1c30d2ae3754c4d88ad...756c76ad6719fde5209ef4bf3b77bd4c1169a44e">compare
view</a></li>
</ul>
</details>
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