Replace local bump-shared-workflow-version with releaser action

[ineedjet]

Once rubykatzen/releaser#58 is done, replace the local .github/actions/bump-shared-workflow-version action with the upstream one from releaser.

Steps

• Wait for Add bump-shared-workflow-version action releaser#58
• Replace uses: ./.github/actions/bump-shared-workflow-version in prepare-release.yml with uses: rubykatzen/releaser/.github/actions/bump-pip-install-version@vX.Y.Z
• Delete .github/actions/bump-shared-workflow-version/

Tracks: rubykatzen/releaser#58