CI: Fix warnings & deprecation messages in the workflows

[ljubon]

What type of PR is this?

CI: Resolve deprecation & warning messages in workflows
Enable DependaBot for GitHub actions

What this PR does / why we need it:

Node16 has been out of support since September 2023. - more info in the post

• Remove dependabot.yaml as dependabot.yml is only one needed
• Bump the steps where deprecation/warnings are shown in the job
• Fix set-output warnings in workflows

Optional

• Resolve on upstream or find alternative for technote-space/create-pr-action@v2 used in Update consul versions workflow

Which issue(s) this PR fixes:

https://github.com/G-Research/gr-oss/issues/636

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Testing results

CI

• no change

CodeQL

• no change

Format

• no change

Nudge

• https://github.com/gr-oss-devops/consuldotnet/actions/runs/9029288911

Deploy website

• no change

Update consul versions

• https://github.com/gr-oss-devops/consuldotnet/actions/runs/9000614756
• NOTE: technote-space/create-pr-action@v2 action is still on Node16, this should be migrated or contributing on the upstream of the action