Auto merge of #27886 - servo:dependabot/cargo/gfx-backend-metal-0.6.5, r=jdm

Bump gfx-backend-metal from 0.6.4 to 0.6.5

Bumps [gfx-backend-metal](https://github.com/gfx-rs/gfx) from 0.6.4 to 0.6.5.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/gfx-rs/gfx/blob/master/CHANGELOG.md">gfx-backend-metal's changelog</a>.</em></p>
<blockquote>
<h3>backend-vulkan-0.6.5 (15-10-2020)</h3>
<ul>
<li>support different types of descriptors in a single <code>DescriptorSetWrite</code></li>
</ul>
<h3>backend-dx12-0.6.3 backend-dx11-0.6.1 backend-metal-0.6.2 auxil-0.5.1 (31-08-2020)</h3>
<ul>
<li>update spirv_cross to 0.21:
<ul>
<li>force zero initialization in all generated shaders</li>
<li>force the use of native arrays for MSL</li>
</ul>
</li>
</ul>
<h3>backend-dx12-0.6.7 (12-10-2020)</h3>
<ul>
<li>get proper support for compressed textures</li>
</ul>
<h3>backend-dx12-0.6.6 (05-10-2020)</h3>
<ul>
<li>allow color blend factors to be used on alpha channel</li>
</ul>
<h3>backend-dx12-0.6.5 (04-10-2020)</h3>
<ul>
<li>implement command buffer markers</li>
<li>debug names for render passes and descriptor sets</li>
</ul>
<h3>backend-vulkan-0.6.3 (30-09-2020)</h3>
<ul>
<li>enable VK_KHR_maintenance3 when VK_EXT_descriptor_indexing is enabled</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li>See full diff in <a href="https://github.com/gfx-rs/gfx/commits">compare view</a></li>
</ul>
</details>
<br />

[![Dependabot compatibility score](https://api.dependabot.com/badges/compatibility_score?dependency-name=gfx-backend-metal&package-manager=cargo&previous-version=0.6.4&new-version=0.6.5)](https://dependabot.com/compatibility-score/?dependency-name=gfx-backend-metal&package-manager=cargo&previous-version=0.6.4&new-version=0.6.5)

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

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</details>

Cargo.lock

@@ -2075,9 +2075,9 @@ dependencies = [
 
 [[package]]
 name = "gfx-backend-metal"
-version = "0.6.4"
+version = "0.6.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "60ba1c77c112e7d35786dbd49ed26f2a76ce53a44bc09fe964935e4e35ed7f2b"
+checksum = "273d60d5207f96d99e0d11d0718995f67e56533a9df1444d83baf787f4c3cb32"
 dependencies = [
  "arrayvec 0.5.1",
  "bitflags",