Error in re-executing workflow files

[m-alisafaee]

Describe the bug
If we run a workflow file partially and then run it again fully, we get a database error.

To Reproduce
Steps to reproduce the behavior:

1. Create a new project
2. Unzip and copy the attached workflow file to the project: workflow-file.yml.zip
3. renku run workflow-file.yml head tail
4. renku run workflow-file.yml

Executing step 'workflow-file.head': 'head -n10 Dockerfile > intermediate' ...
Executing step 'workflow-file.tail': 'tail -n5 intermediate > results/output.csv' ...
Executing step 'workflow-file.line-count': 'wc -l results/output.csv > results/output.csv.wc' ...
Ahhhhhhhh! You have found a bug. �

1. Open an issue by typing "open";
2. Print human-readable information by typing "print";
3. See the full traceback without submitting details (default: "ignore").

Please select an action by typing its name (open, print, ignore) [ignore]: 
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.9/bin/renku", line 8, in <module>
    sys.exit(cli())
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/ui/cli/exception_handler.py", line 141, in main
    self._handle_github()
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/ui/cli/exception_handler.py", line 173, in _handle_github
    getattr(self, "_process_" + value)()
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/ui/cli/exception_handler.py", line 133, in main
    return super().main(*args, **kwargs)
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/ui/cli/exception_handler.py", line 92, in main
    return super().main(*args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/click/core.py", line 1657, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/ui/cli/run.py", line 612, in run
    run_workflow_file_command(no_commit=no_commit, commit_only=commit_only)
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/command/command_builder/command.py", line 266, in execute
    hook(self, context, result, *args, **kwargs)
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/command/command_builder/database.py", line 112, in _post_hook
    project_context.pop_context()
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/domain_model/project_context.py", line 244, in pop_context
    self._top.database.commit()
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/infrastructure/database.py", line 454, in commit
    self._store_object(object)
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/infrastructure/database.py", line 461, in _store_object
    self._cache[object._p_oid] = object
  File "/Users/Mohammad/Documents/Workspace.noindex/sdsc/code/renku-python/renku/infrastructure/database.py", line 527, in __setitem__
    raise ValueError(f"The same oid exists: {existing_data} != {object}")
ValueError: The same oid exists: <WorkflowFilePlan 'workflow-file.line-count'> != <WorkflowFilePlan 'workflow-file.line-count'>

Additional context
Renku should reuse the existing WorkflowFilePlan but it creates a new instance with the same ID which causes this error.