chore(docs): fix code block language to shell (#28895)

Author: muescha

benchmarks/source-strapi/README.md

@@ -8,6 +8,6 @@ Create a .env file from the template:
 
 Update data:
 
-```sh
+```shell
 yarn date-update
 ```

docs/docs/how-to/styling/using-web-fonts.md

@@ -53,13 +53,13 @@ You can add Typekit Web Fonts to your project by using the [gatsby-plugin-web-fo
 
 First, install the Gatsby plugin with npm:
 
-```bash
+```shell
 npm install --save gatsby-plugin-web-font-loader
 ```
 
 Or with yarn:
 
-```bash
+```shell
 yarn add gatsby-plugin-web-font-loader
 ```
 

packages/gatsby-admin/README.md

@@ -6,7 +6,7 @@ A visual interface to configure your Gatsby site. Currently alpha testing.
 
 For now, Gatsby Admin is marked as experimental and requires a flag to enable. Add the following flag when using `gatsby develop`:
 
-```sh
+```shell
 GATSBY_EXPERIMENTAL_ENABLE_ADMIN=true gatsby develop
 ```
 
@@ -98,7 +98,7 @@ The easiest way to work on Admin locally is to develop Admin itself.
 
 To try Admin with one of your sites locally, use the `gatsby-dev-cli` to copy the local versions of `gatsby`, `gatsby-cli`, `gatsby-recipes`, `gatsby-core-utils` and `gatsby-admin` into your project:
 
-```sh
+```shell
 # Make sure to build the latest local versions of all packages
 ~/gatsby
 yarn run watch

packages/gatsby-recipes/CONTRIBUTING.md

@@ -114,7 +114,7 @@ One note, as you’ll be testing changes to the Gatsby CLI — instead of runnin
 
 When debugging the CLI, you may run into errors without stacktraces. In order to work around that, you can use the node inspector:
 
-```sh
+```shell
 DEBUG=true node --inspect-brk ./node_modules/.bin/gatsby recipes ./test.mdx
 ```
 

starters/gatsby-starter-mdx-basic/README.md

@@ -6,19 +6,19 @@ README also applies here.
 
 1. Create a new Gatsby site using this starter
 
-```sh
+```shell
 gatsby new my-site https://github.com/gatsbyjs/gatsby-starter-mdx-basic
 ```
 
 2. Install dependencies
 
-```sh
+```shell
 npm install
 ```
 
 3. Run the develop script
 
-```sh
+```shell
 gatsby develop
 ```