ci: Switch from BuildJet to GitHub runners (#35826)

In response to an ongoing BuildJet outage, consider migrating CI to
GitHub hosted runners.

Also includes revert of (causing flaky tests):
- https://github.com/zed-industries/zed/pull/35741

Downsides:
- Cost (2x)
- Force migration to Ubuntu 22.04 from 20.04 will bump our glibc minimum
from 2.31 to 2.35. Which would break RHEL 9.x (glibc 2.34), Ubuntu 20.04
(EOL) and derivatives.

Release Notes:

- N/A

.github/actions/build_docs/action.yml

@@ -13,7 +13,7 @@ runs:
       uses: swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2
       with:
         save-if: ${{ github.ref == 'refs/heads/main' }}
-        cache-provider: "buildjet"
+        # cache-provider: "buildjet"
 
     - name: Install Linux dependencies
       shell: bash -euxo pipefail {0}