Upgrade postcss

Author: rbottomley

yarn.lock

@@ -11409,7 +11409,16 @@ postcss@^8.2.15, postcss@^8.2.9, postcss@^8.3.11:
     picocolors "^1.0.0"
     source-map-js "^1.0.2"
 
-postcss@^8.3.9, postcss@^8.4.18:
+postcss@^8.3.9:
+  version "8.4.20"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.20.tgz#64c52f509644cecad8567e949f4081d98349dc56"
+  integrity sha512-6Q04AXR1212bXr5fh03u8aAwbLxAQNGQ/Q1LNa0VfOI06ZAlhPHtQvE4OIdpj4kLThXilalPnmDSOD65DcHt+g==
+  dependencies:
+    nanoid "^3.3.4"
+    picocolors "^1.0.0"
+    source-map-js "^1.0.2"
+
+postcss@^8.4.18:
   version "8.4.19"
   resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.19.tgz#61178e2add236b17351897c8bcc0b4c8ecab56fc"
   integrity sha512-h+pbPsyhlYj6N2ozBmHhHrs9DzGmbaarbLvWipMRO7RLS+v4onj26MPFXA5OBYFxyqYhUJK456SwDcY9H2/zsA==