[7.17] Upgrade postcss@8.4.14→8.4.31 (#167815) (#167921)

# Backport

This will backport the following commits from `main` to `7.17`:
- [Upgrade postcss@8.4.14→8.4.31
(#167815)](#167815)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Jeramy
Soucy","email":"jeramy.soucy@elastic.co"},"sourceCommit":{"committedDate":"2023-10-03T18:16:42Z","message":"Upgrade
postcss@8.4.14→8.4.31 (#167815)\n\n## Summary\r\n\r\nUpgrades dev-only
dependency `postcss` where possible (v8.4.14
to\r\nv8.4.31).","sha":"60f66eaf06cd92967cb569a577b50d83e4c94b12","branchLabelMapping":{"^v8.11.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Security","release_note:skip","v8.1.1","backport:all-open","v8.11.0"],"number":167815,"url":"#167815
postcss@8.4.14→8.4.31 (#167815)\n\n## Summary\r\n\r\nUpgrades dev-only
dependency `postcss` where possible (v8.4.14
to\r\nv8.4.31).","sha":"60f66eaf06cd92967cb569a577b50d83e4c94b12"}},"sourceBranch":"main","suggestedTargetBranches":["8.1"],"targetPullRequestStates":[{"branch":"8.1","label":"v8.1.1","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"main","label":"v8.11.0","labelRegex":"^v8.11.0$","isSourceBranch":true,"state":"MERGED","url":"#167815
postcss@8.4.14→8.4.31 (#167815)\n\n## Summary\r\n\r\nUpgrades dev-only
dependency `postcss` where possible (v8.4.14
to\r\nv8.4.31).","sha":"60f66eaf06cd92967cb569a577b50d83e4c94b12"}}]}]
BACKPORT-->

---------

Co-authored-by: Jeramy Soucy <jeramy.soucy@elastic.co>

package.json

@@ -785,7 +785,7 @@
     "pixelmatch": "^5.3.0",
     "playwright": "^1.17.1",
     "pngjs": "^3.4.0",
-    "postcss": "^8.4.14",
+    "postcss": "^8.4.31",
     "postcss-loader": "^4.2.0",
     "postcss-prefix-selector": "^1.16.0",
     "prettier": "^2.7.1",

yarn.lock

@@ -20598,7 +20598,7 @@ nanoid@3.3.3:
   resolved "https://registry.yarnpkg.com/nanoid/-/nanoid-3.3.3.tgz#fd8e8b7aa761fe807dba2d1b98fb7241bb724a25"
   integrity sha512-p1sjXuopFs0xg+fPASzQ28agW1oHD7xDsd9Xkf3T15H3c/cifrFHVwrh74PdoklAPi+i7MdRsE47vm2r6JoB+w==
 
-nanoid@^3.3.1, nanoid@^3.3.4:
+nanoid@^3.3.1:
   version "3.3.4"
   resolved "https://registry.yarnpkg.com/nanoid/-/nanoid-3.3.4.tgz#730b67e3cd09e2deacf03c027c81c9d9dbc5e8ab"
   integrity sha512-MqBkQh/OHTS2egovRtLk45wEyNXwF+cokD+1YPf9u5VfJiRdAiRwB2froX5Co9Rh20xs4siNPm8naNotSD6RBw==
@@ -22725,19 +22725,10 @@ postcss@^7.0.14, postcss@^7.0.16, postcss@^7.0.2, postcss@^7.0.21, postcss@^7.0.
     picocolors "^0.2.1"
     source-map "^0.6.1"
 
-postcss@^8.4.14:
-  version "8.4.14"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.14.tgz#ee9274d5622b4858c1007a74d76e42e56fd21caf"
-  integrity sha512-E398TUmfAYFPBSdzgeieK2Y1+1cpdxJx8yXbK/m57nRhKSmk1GB2tO4lbLBtlkfPQTDKfe4Xqv1ASWPpayPEig==
-  dependencies:
-    nanoid "^3.3.4"
-    picocolors "^1.0.0"
-    source-map-js "^1.0.2"
-
-postcss@^8.4.23:
-  version "8.4.25"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.25.tgz#4a133f5e379eda7f61e906c3b1aaa9b81292726f"
-  integrity sha512-7taJ/8t2av0Z+sQEvNzCkpDynl0tX3uJMCODi6nT3PfASC7dYCWV9aQ+uiCf+KBD4SEFcu+GvJdGdwzQ6OSjCw==
+postcss@^8.4.23, postcss@^8.4.31:
+  version "8.4.31"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.31.tgz#92b451050a9f914da6755af352bdc0192508656d"
+  integrity sha512-PS08Iboia9mts/2ygV3eLpY5ghnUcfLV/EXTOW1E2qYxJKGGBUtNjN76FYHnMs36RmARn41bC0AZmn+rR0OVpQ==
   dependencies:
     nanoid "^3.3.6"
     picocolors "^1.0.0"