Stop update krew for release-1.7, release-1.8

[RainbowMango]

What would you like to be added:

• Remove update-krew-index from branch release-1.7. (Stop krew update for release-1.7 #4767)
• Remove update-krew-index from branch release-1.8. (Stop krew update for release-1.8 #4768)

Why is this needed:
Since krew only caches the latest release, so we don't need to update it for v1.7.x/1.8.x releases. Otherwise, it will open an invalid PR, like kubernetes-sigs/krew-index#2809.

Sample PR: #4023

[ahmetb]

Instead, consider adding a tag filter to the workflow to only run on non-prerelease + v* tags.

[RainbowMango]

Yeah, I'm still thinking this.
I guess this might be a common issue for Krew, do you know where I can find an example about how to add the filter?

I'm not sure if it will work if add a filter something like:

  update-krew-index:
    if: <latest release>   // Not sure how to write the logic yet.
    needs: release-assests
    name: Update krew-index
    runs-on: ubuntu-22.04
    steps:
    - uses: actions/checkout@v3
    - name: Update new version in krew-index
      uses: rajatjindal/krew-release-bot@v0.0.40