Set progress no update

[leeagustin]

Fixes #2846.

While I wasn't able to replicate the error from the issue, I did find that set_progress((no_update, str(total))) sets the progress to 0:

This is because the progress bar's value is being set to "[object Object]", which is probably being interpreted as 0. The progress bar's HTML being: <progress id="progress_bar" value="[object Object]" max="5" style="visibility: visible;"></progress>.

I modified it so that if set_progress has no_update for a component's output, that component will not be updated, but the other components—assuming they are not no_update—will be updated.

Contributor Checklist

• [x] I have broken down my PR scope into the following TODO tasks
  • [x] Allows for no_update in background callback set_progress
• [x] I have run the tests locally and they passed. (refer to testing section in contributing)
• [x] I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• [ ] I have added entry in the CHANGELOG.md
• [ ] If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • [ ] this GitHub #PR number updates the dash docs
  • [ ] here is the show and tell thread in Plotly Dash community