Disable ec2 runners on PR (#1357)

#### Reference Issues/PRs
<!--Example: Fixes #1234. See also #3456.-->

#### What does this implement or fix?
Makes it so ec2 runners are used for benchmarks only during the
scheduled runs

#### Any other comments?

#### Checklist

<details>
  <summary>
   Checklist for code changes...
  </summary>
 
- [ ] Have you updated the relevant docstrings, documentation and
copyright notice?
- [ ] Is this contribution tested against [all ArcticDB's
features](../docs/mkdocs/docs/technical/contributing.md)?
- [ ] Do all exceptions introduced raise appropriate [error
messages](https://docs.arcticdb.io/error_messages/)?
 - [ ] Are API changes highlighted in the PR description?
- [ ] Is the PR labelled as enhancement or bug so it appears in
autogenerated release notes?
</details>

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.github/workflows/analysis_workflow.yml

@@ -192,13 +192,15 @@ jobs:
  SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK
 
  start_ec2_runner:
+ if: github.event_name == 'schedule'
  uses: ./.github/workflows/ec2_runner_jobs.yml
  secrets: inherit
  with:
  job_type: start
 
  benchmark_linux_medium:
  timeout-minutes: 1200
+ if: github.event_name == 'schedule'
  needs: [start_ec2_runner, cibw_docker_image]
  runs-on: ${{ needs.start_ec2_runner.outputs.label }}
  container:
@@ -238,7 +240,7 @@ jobs:
  echo /opt/python/cp36-cp36m/bin >> $GITHUB_PATH
 
  - name: Install ASV
- shell: bash
+ shell: bash -el {0}
  run: |
  git config --global --add safe.directory .
  python -m pip install --upgrade pip
@@ -288,7 +290,7 @@ jobs:
 
  stop-ec2-runner:
  needs: [start_ec2_runner, benchmark_linux_medium]
- if: ${{ always() }}
+ if: github.event_name == 'schedule'
  uses: ./.github/workflows/ec2_runner_jobs.yml
  secrets: inherit
  with: