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/workflows/unit_evals.yml

@@ -23,7 +23,7 @@ jobs:
     timeout-minutes: 60
     name: Run unit evals
     runs-on:
-      - buildjet-16vcpu-ubuntu-2204
+      - github-16vcpu-ubuntu-2204
     steps:
       - name: Add Rust to the PATH
         run: echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
@@ -37,7 +37,7 @@ jobs:
         uses: swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2
         with:
           save-if: ${{ github.ref == 'refs/heads/main' }}
-          cache-provider: "buildjet"
+          # cache-provider: "buildjet"
 
       - name: Install Linux dependencies
         run: ./script/linux