diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f54e06616f76..f5f812e2a2db 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -56,12 +56,11 @@ jobs:
           fi
 
   test-each-commit:
-    name: 'test max 6 ancestor commits'
-    runs-on: ubuntu-24.04
+    name: 'test ancestor commits'
+    needs: runners
+    runs-on: ${{ needs.runners.outputs.provider == 'cirrus' && 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-md' || 'ubuntu-24.04' }}
     if: github.event_name == 'pull_request' && github.event.pull_request.commits != 1
-    timeout-minutes: 360  # Use maximum time, see https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#jobsjob_idtimeout-minutes. Assuming a worst case time of 1 hour per commit, this leads to a --max-count=6 below.
-    env:
-      MAX_COUNT: 6  # Keep in sync with name above
+    timeout-minutes: 360  # Use maximum time, see https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#jobsjob_idtimeout-minutes.
     steps:
       - name: Determine fetch depth
         run: echo "FETCH_DEPTH=$((${{ github.event.pull_request.commits }} + 2))" >> "$GITHUB_ENV"
@@ -77,14 +76,8 @@ jobs:
           # head commit that are already run by other jobs.
           git checkout HEAD~
           # Figure out test base commit by listing ancestors of HEAD, excluding
-          # ancestors of the most recent merge commit, limiting the list to the
-          # newest MAX_COUNT ancestors, ordering it from oldest to newest, and
-          # taking the first one.
-          #
-          # If the branch contains up to MAX_COUNT ancestor commits after the
-          # most recent merge commit, all of those commits will be tested. If it
-          # contains more, only the most recent MAX_COUNT commits will be
-          # tested.
+          # ancestors of the most recent merge commit, ordering it from oldest to
+          # newest, and taking the first one.
           #
           # In the command below, the ^@ suffix is used to refer to all parents
           # of the merge commit as described in:
@@ -98,7 +91,7 @@ jobs:
           if test -n "$MERGE_BASE"; then
             EXCLUDE_MERGE_BASE_ANCESTORS=^${MERGE_BASE}^@
           fi
-          echo "TEST_BASE=$(git rev-list -n$((${{ env.MAX_COUNT }} + 1)) --reverse HEAD $EXCLUDE_MERGE_BASE_ANCESTORS | head -1)" >> "$GITHUB_ENV"
+          echo "TEST_BASE=$(git rev-list -n${{ github.event.pull_request.commits }} --reverse HEAD $EXCLUDE_MERGE_BASE_ANCESTORS | head -1)" >> "$GITHUB_ENV"
       - run: |
           git fetch origin "${GITHUB_BASE_REF}"
           git config user.email "ci@example.com"