workflows/eval: drop process job

Since process doesn't need to run on push events anymore, we can just as
well remove it entirely. The little bit of combine and comparison can be
done in the tag job, even with elevated privileges. That's because those
parts can be done entirely from the target commit, which is trusted.

This saves startup, installing nix, downloading tools and artifacts for
one job. It saves about 1 minute per run, start to finish.

(cherry picked from commit b942fb47dc)

.github/workflows/eval.yml

@@ -153,11 +153,14 @@ jobs:
           name: diff-${{ matrix.system }}
           path: diff/*
 
-  process:
-    name: Process
+  tag:
+    name: Tag
     runs-on: ubuntu-24.04-arm
     needs: [ prepare, outpaths ]
     if: needs.prepare.outputs.targetSha
+    permissions:
+      pull-requests: write
+      statuses: write
     steps:
       - name: Download output paths and eval stats for all systems
         uses: actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16 # v4.1.8
@@ -206,46 +209,6 @@ jobs:
           name: comparison
           path: comparison/*
 
-  # Separate job to have a very tightly scoped PR write token
-  tag:
-    name: Tag
-    runs-on: ubuntu-24.04-arm
-    needs: [ prepare, process ]
-    if: needs.prepare.outputs.targetSha
-    permissions:
-      pull-requests: write
-      statuses: write
-    steps:
-      # See ./codeowners-v2.yml, reuse the same App because we need the same permissions
-      # Can't use the token received from permissions above, because it can't get enough permissions
-      - uses: actions/create-github-app-token@df432ceedc7162793a195dd1713ff69aefc7379e # v2.0.6
-        if: vars.OWNER_APP_ID
-        id: app-token
-        with:
-          app-id: ${{ vars.OWNER_APP_ID }}
-          private-key: ${{ secrets.OWNER_APP_PRIVATE_KEY }}
-          permission-administration: read
-          permission-members: read
-          permission-pull-requests: write
-
-      - name: Download comparison result
-        uses: actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16 # v4.1.8
-        with:
-          name: comparison
-          path: comparison
-
-      - name: Install Nix
-        uses: cachix/install-nix-action@526118121621777ccd86f79b04685a9319637641 # v31
-
-      # Important: This workflow job runs with extra permissions,
-      # so we need to make sure to not run untrusted code from PRs
-      - name: Check out Nixpkgs at the target commit
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-        with:
-          ref: ${{ needs.prepare.outputs.targetSha }}
-          path: trusted
-          sparse-checkout: ci
-
       - name: Build the requestReviews derivation
         run: nix-build trusted/ci -A requestReviews
 
@@ -303,6 +266,18 @@ jobs:
             "/repos/$GITHUB_REPOSITORY/statuses/$PR_HEAD_SHA" \
             -f "context=Eval / Summary" -f "state=success" -f "description=$description" -f "target_url=$target_url"
 
+      # See ./codeowners-v2.yml, reuse the same App because we need the same permissions
+      # Can't use the token received from permissions above, because it can't get enough permissions
+      - uses: actions/create-github-app-token@df432ceedc7162793a195dd1713ff69aefc7379e # v2.0.6
+        if: vars.OWNER_APP_ID
+        id: app-token
+        with:
+          app-id: ${{ vars.OWNER_APP_ID }}
+          private-key: ${{ secrets.OWNER_APP_PRIVATE_KEY }}
+          permission-administration: read
+          permission-members: read
+          permission-pull-requests: write
+
       - name: Requesting maintainer reviews
         if: ${{ steps.app-token.outputs.token && github.repository_owner == 'NixOS' }}
         env: