build(deps): Bump postcss from 8.5.8 to 8.5.15 in /client

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.8 to 8.5.15.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.5.8...8.5.15)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.15
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

client/package-lock.json

@@ -13747,9 +13747,9 @@
       }
     },
     "node_modules/postcss": {
-      "version": "8.5.8",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.8.tgz",
-      "integrity": "sha512-OW/rX8O/jXnm82Ey1k44pObPtdblfiuWnrd8X7GJ7emImCOstunGbXUpp7HdBrFQX6rJzn3sPT397Wp5aCwCHg==",
+      "version": "8.5.15",
+      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.15.tgz",
+      "integrity": "sha512-FfR8sjd4em2T6fb3I2MwAJU7HWVMr9zba+enmQeeWFfCbm+UOC/0X4DS8XtpUTMwWMGbjKYP7xjfNekzyGmB3A==",
       "funding": [
         {
           "type": "opencollective",
@@ -13766,7 +13766,7 @@
       ],
       "license": "MIT",
       "dependencies": {
-        "nanoid": "^3.3.11",
+        "nanoid": "^3.3.12",
         "picocolors": "^1.1.1",
         "source-map-js": "^1.2.1"
       },
@@ -13775,9 +13775,9 @@
       }
     },
     "node_modules/postcss/node_modules/nanoid": {
-      "version": "3.3.11",
-      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.11.tgz",
-      "integrity": "sha512-N8SpfPUnUp1bK+PMYW8qSWdl9U+wwNWI4QKxOYDy9JAro3WMX7p2OeVRF9v+347pnakNevPmiHhNmZ2HbFA76w==",
+      "version": "3.3.12",
+      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.12.tgz",
+      "integrity": "sha512-ZB9RH/39qpq5Vu6Y+NmUaFhQR6pp+M2Xt76XBnEwDaGcVAqhlvxrl3B2bKS5D3NH3QR76v3aSrKaF/Kiy7lEtQ==",
       "funding": [
         {
           "type": "github",