Update dependency postcss to ^8.5.6 (main) (#235642)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [postcss](https://postcss.org/)
([source](https://redirect.github.com/postcss/postcss)) |
devDependencies | patch | [`^8.5.3` ->
`^8.5.6`](https://renovatebot.com/diffs/npm/postcss/8.5.4/8.5.6) |

---

### Release Notes

<details>
<summary>postcss/postcss (postcss)</summary>

###
[`v8.5.6`](https://redirect.github.com/postcss/postcss/blob/HEAD/CHANGELOG.md#856)

[Compare
Source](https://redirect.github.com/postcss/postcss/compare/8.5.5...8.5.6)

- Fixed `ContainerWithChildren` type discriminating (by
[@&#8203;Goodwine](https://redirect.github.com/Goodwine)).

###
[`v8.5.5`](https://redirect.github.com/postcss/postcss/blob/HEAD/CHANGELOG.md#855)

[Compare
Source](https://redirect.github.com/postcss/postcss/compare/8.5.4...8.5.5)

- Fixed `package.json`→`exports` compatibility with some tools (by
[@&#8203;JounQin](https://redirect.github.com/JounQin)).

</details>

---

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---

This PR has been generated by [Renovate
Bot](https://redirect.github.com/renovatebot/renovate).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzOS4xMDcuMCIsInVwZGF0ZWRJblZlciI6IjM5LjEwNy4wIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJUZWFtOk9wZXJhdGlvbnMiLCJiYWNrcG9ydDphbGwtb3BlbiIsInJlbGVhc2Vfbm90ZTpza2lwIl19-->

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Co-authored-by: elastic-renovate-prod[bot] <174716857+elastic-renovate-prod[bot]@users.noreply.github.com>
Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
(cherry picked from commit ad5c525)

Author: elastic-renovate-prod[bot]

package.json

@@ -1886,7 +1886,7 @@
     "pixelmatch": "^5.3.0",
     "playwright": "1.53.1",
     "pngjs": "^7.0.0",
-    "postcss": "^8.5.3",
+    "postcss": "^8.5.6",
     "postcss-loader": "^8.1.1",
     "postcss-prefix-selector": "^1.16.0",
     "postcss-scss": "^4.0.9",

yarn.lock

@@ -27136,10 +27136,10 @@ postcss@8.4.31:
     picocolors "^1.0.0"
     source-map-js "^1.0.2"
 
-postcss@^8.4.19, postcss@^8.4.23, postcss@^8.4.33, postcss@^8.5.3:
-  version "8.5.4"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.5.4.tgz#d61014ac00e11d5f58458ed7247d899bd65f99c0"
-  integrity sha512-QSa9EBe+uwlGTFmHsPKokv3B/oEMQZxfqW0QqNCyhpa6mB1afzulwn8hihglqAb2pOw+BJgNlmXQ8la2VeHB7w==
+postcss@^8.4.19, postcss@^8.4.23, postcss@^8.4.33, postcss@^8.5.6:
+  version "8.5.6"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.5.6.tgz#2825006615a619b4f62a9e7426cc120b349a8f3c"
+  integrity sha512-3Ybi1tAuwAP9s0r1UQ2J4n5Y0G05bJkpUIO0/bI9MhwmD70S5aTWbXGBwxHrelT+XM1k6dM0pk+SwNkpTRN7Pg==
   dependencies:
     nanoid "^3.3.11"
     picocolors "^1.1.1"