chore: Add missing code fence languages (#772)

* chore: Add missing code fence languages

* Update content/actions/creating-actions/dockerfile-support-for-github-actions.md

* Add raw & endraw markers around shell content

See review comment by @rachmari

* Add raw & endraw markers around shell content

See review comment by @rachmari

* Remove language from code fences

to avoid the problem of replaceable text indicates like
<this> not showing up in the output page.

Co-authored-by: hubwriter <hubwriter@github.com>

content/github/working-with-github-pages/about-github-pages-and-jekyll.md

@@ -38,7 +38,7 @@ You can configure most Jekyll settings, such as your site's theme and plugins, b
 
 Some configuration settings cannot be changed for {% data variables.product.prodname_pages %} sites.
 
-```
+```yaml
 lsi: false
 safe: true
 source: [your repo's top level directory]
@@ -111,7 +111,7 @@ By default, code blocks on your site will be highlighted by Jekyll. Jekyll uses
 
 If you want to use another highlighter, such as `highlight.js`, you must disable Jekyll's syntax highlighting by updating your project's *_config.yml* file.
 
-```
+```yaml
 kramdown:
   syntax_highlighter_opts:
     disable : true

content/github/working-with-github-pages/about-jekyll-build-errors-for-github-pages-sites.md

@@ -44,13 +44,13 @@ You can see build failures (but not build warnings) for your site on {% data var
 You can configure a third-party service, such as [Travis CI](https://travis-ci.org/), to display error messages after each commit.
 
 1. If you haven't already, add a file called _Gemfile_ in the root of your publishing source, with the following content:
-  ```
+  ```ruby
   source `https://rubygems.org`
   gem `github-pages`
   ```
 
 2. Configure your site's repository for the testing service of your choice. For example, to use [Travis CI](https://travis-ci.org/), add a file named _.travis.yml_ in the root of your publishing source, with the following content:
-  ```
+  ```yaml
   language: ruby
   rvm:
     - 2.3

content/github/working-with-github-pages/adding-a-theme-to-your-github-pages-site-using-jekyll.md

@@ -42,7 +42,7 @@ People with write permissions for a repository can add a theme to a {% data vari
 {% data reusables.pages.navigate-publishing-source %}
 1. Create a new file called _/assets/css/style.scss_.
 2. Add the following content to the top of the file:
-  ```
+  ```scss
   ---
   ---
 

content/github/working-with-github-pages/creating-a-custom-404-page-for-your-github-pages-site.md

@@ -17,7 +17,7 @@ versions:
 3. In the file name field, type `404.html` or `404.md`.
   ![File name field](/assets/images/help/pages/404-file-name.png)
 4. If you named your file `404.md`, add the following YAML front matter to the beginning of the file:
-  ```
+  ```yaml
   ---
   permalink: /404.html
   ---

content/github/working-with-github-pages/troubleshooting-jekyll-build-errors-for-github-pages-sites.md

@@ -78,7 +78,7 @@ This error means that your code references a symlinked file that does not exist
 This error means that you used non-Latin characters, like `日本語`, without telling the computer to expect these symbols.
 
 To troubleshoot, force UTF-8 encoding by adding the following line to your *_config.yml* file:
-```
+```yaml
 encoding: UTF-8
 ```