docs(guide): Fix heirarchy for CI

Things were flat due to the nesting level they were at and this was
overlooked when changing the levels in rust-lang#12595

src/doc/src/guide/continuous-integration.md

@@ -4,7 +4,7 @@
 
 A basic CI will build and test your projects:
 
-## GitHub Actions
+### GitHub Actions
 
 To test your package on GitHub Actions, here is a sample `.github/workflows/ci.yml` file:
 
@@ -38,7 +38,7 @@ jobs:
 
 This will test all three release channels (note a failure in any toolchain version will fail the entire job). You can also click `"Actions" > "new workflow"` in the GitHub UI and select Rust to add the [default configuration](https://github.com/actions/starter-workflows/blob/main/ci/rust.yml) to your repo. See [GitHub Actions documentation](https://docs.github.com/en/actions) for more information.
 
-## GitLab CI
+### GitLab CI
 
 To test your package on GitLab CI, here is a sample `.gitlab-ci.yml` file:
 
@@ -67,7 +67,7 @@ breakage in nightly will not fail your overall build. Please see the
 [GitLab CI documentation](https://docs.gitlab.com/ce/ci/yaml/index.html) for more
 information.
 
-## builds.sr.ht
+### builds.sr.ht
 
 To test your package on sr.ht, here is a sample `.build.yml` file.
 Be sure to change `<your repo>` and `<your project>` to the repo to clone and