[code-infra] Remove some csbci references (#46797)

Signed-off-by: Olivier Tassinari <oliviertassinari@users.noreply.github.com>
Co-authored-by: Olivier Tassinari <olivier.tassinari@gmail.com>
Co-authored-by: Olivier Tassinari <oliviertassinari@users.noreply.github.com>

Author: Janpot

CONTRIBUTING.md

@@ -178,10 +178,9 @@ For CircleCI, you need to log in first.
 No further permissions are required to view the build logs.
 The following sections give an overview of what each check is responsible for.
 
-#### ci/codesandbox
+#### Continuous Releases
 
-This task creates multiple sandboxes on CodeSandbox.com that use the version of npm packages that was built from this pull request.
-It should not fail in isolation. Use it to test more complex scenarios.
+This task publishes a preview for the packages to pkg.pr.new. It should not fail in isolation. Use it to test more complex scenarios.
 
 #### ci/circleci: checkout
 
@@ -329,9 +328,9 @@ Check out [this Toggle Button demo PR](https://github.com/mui/material-ui/pull/1
 
 ## How can I use a change that hasn't been released yet?
 
-We use [CodeSandbox CI](https://codesandbox.io/docs/ci) to publish a working version of the packages for each pull request as a "preview."
+We use [pkg.pr.new](https://pkg.pr.new) to publish a working version of the packages for each pull request as a "preview."
 
-You can check the CodeSandbox CI status of a pull request to get the URL needed to install these preview packages:
+You can check the _Continuous Releases_ status of a pull request to get the URL needed to install these preview packages:
 
 ```diff
 diff --git a//package.json b//package.json
@@ -343,11 +342,11 @@ index 791a7da1f4..a5db13b414 100644
      "@babel/runtime": "^7.4.4",
      "@mui/styled-engine": "^5.0.0-alpha.16",
 -    "@mui/material": "^5.0.0-alpha.15",
-+    "@mui/material": "https://pkg.csb.dev/mui/material-ui/commit/371c952b/@mui/material",
++    "@mui/material": "https://pkg.pr.new/mui/material-ui/@mui/material@b0f26aa",
      "@mui/system": "^5.0.0-alpha.16",
 ```
 
-Alternatively, you can open the Netlify preview of the documentation, and open any demo in CodeSandbox.
+Alternatively, you can open the Netlify preview of the documentation, and open any demo in CodeSandbox or StackBlitz.
 The documentation automatically configures the dependencies to use the preview packages.
 
 You can also package and test your changes locally.

test/bundling/README.md

@@ -19,7 +19,7 @@ The created file might need some manual adjustment since not every edge case is
 
 ### To test a published npm dist tag
 
-_For example: `latest` or `next` on npm or a codesandboxci published version_
+_For example: `latest` or `next` on npm or a pkg.pr.new published version_
 
 1. Navigate into the fixture you want to test (where the `package.json` is located)
 1. Adjust `pnpm.overrides` of the `package.json` file to point to the desired version