fix: upgrade gatsby and deps to 4.21.0 (#10784)

* fix: upgrade `gatsby` to 4.21.0 to fix Firefox dev

on `gatsby` 4.19.0, Firefox won't render the site in development
if there are any runtime errors. this was fixed in 4.21.0.
see gatsbyjs/gatsby#36365

* upgrade Gatsby core dependencies to 4.21.0

package.json

@@ -15,26 +15,26 @@
     "common-tags": "^1.8.0",
     "date-fns": "^2.17.0",
     "front-matter": "^4.0.2",
-    "gatsby": "~4.19.0",
+    "gatsby": "4.21.0",
     "gatsby-image": "^3.11.0",
-    "gatsby-plugin-gatsby-cloud": "~4.19.0",
+    "gatsby-plugin-gatsby-cloud": "4.21.0",
     "gatsby-plugin-json-output": "^1.2.0",
-    "gatsby-plugin-manifest": "~4.19.0",
+    "gatsby-plugin-manifest": "4.21.0",
     "gatsby-plugin-mdx": "3.4.0",
     "gatsby-plugin-meta-redirect": "^1.1.1",
     "gatsby-plugin-offline": "^5.4.0",
     "gatsby-plugin-react-helmet": "^5.4.0",
-    "gatsby-plugin-sharp": "~4.19.0",
+    "gatsby-plugin-sharp": "4.21.0",
     "gatsby-remark-autolink-headers": "^5.4.0",
     "gatsby-remark-copy-linked-files": "^5.4.0",
     "gatsby-remark-images": "^6.4.0",
-    "gatsby-source-filesystem": "~4.19.0",
-    "gatsby-transformer-json": "~4.19.0",
+    "gatsby-source-filesystem": "4.21.0",
+    "gatsby-transformer-json": "4.21.0",
     "gatsby-transformer-plaintext": "^2.0.0",
     "gatsby-transformer-remark": "^5.4.0",
-    "gatsby-transformer-sharp": "~4.19.0",
+    "gatsby-transformer-sharp": "4.21.0",
     "gatsby-transformer-xml": "^4.24.0",
-    "gatsby-transformer-yaml": "~4.19.0",
+    "gatsby-transformer-yaml": "4.21.0",
     "github-slugger": "^1.3.0",
     "hast-util-from-dom": "^3.0.0",
     "hast-util-has-property": "^1.0.4",