Is there a way to delete a github workflow

Yes, you can delete all the workflow runs in the workflow which you want to delete, then this workflow will disappear.

Yes, you can delete the results of a run. See the documentation for details.

To delete a particular workflow on your Actions page, you need to delete all runs which belong to this workflow. Otherwise it persists even if you have deleted the YAML file that had been triggered it.

If you have just a couple of runs in a particular action, it's easier to delete them manually. But if you have a hundred of runs, it might worth running a simple script. For example, the following python script uses GitHub API:

Before you start, you need to define three things:

1. PAT: create a new personal access GitHub token;
2. your repo name
3. your action name (even you got deleted it already, just hover over the action on the actions page):

from github import Github
import requests

token = "ghp_1234567890abcdefghij1234567890123456" # your PAT
repo = "octocat/my_repo"
action = "my_action.yml"

g = Github(token)
headers = {'Accept': 'application/vnd.github.v3',
           'Authorization': f'token {token}'}

for run in g.get_repo(repo).get_workflow(id_or_name=action).get_runs():
    response = requests.delete(url=run.url, headers=headers)
    if response.status_code == 204:
        print(f"Run {run.id} got deleted")

Don't forget to run pip install PyGithub upfront.

After all runs are deleted, the workflow automatically disappears from the page.

https://docs.github.com/en/rest/reference/actions#delete-a-workflow-run

To delete programmatically

Example (from the docs)

curl \
  -X DELETE \
  -H "Authorization: token <PERSONAL_ACCESS_TOKEN>"
  -H "Accept: application/vnd.github.v3+json" \
  https://api.github.com/repos/octocat/hello-world/actions/runs/42