fix: tests-pytest/action.yml: inputs: add skip-install

[anscfrisson]

This PR proposes add a missing definition of the skip-install input in tests-pytest/action.yml:

  skip-install:
    description: >
      Whether to skip install. 
      Should be false with poetry as build-backend.
      The default value is ``false``.
    default: false
    required: false
    type: boolean

Noticed with https://github.com/ansys-internal/simba-core/actions/runs/8327410143/job/22785207488

Run if grep -q 'build-backend = "poetry\.core\.masonry\.api"' "pyproject.toml"; then
/home/runner/work/_temp/508acb6f-5ce8-452e-84cd-fd2b2305b3de.sh: line 2: poetry: command not found

This is because inputs.skip-install does not exist, then this step that installs poetry is skipped in tests-pytest/action.yml

    - name: "Install project (if required)"
      if: inputs.skip-install == 'false'
      shell: bash
      run: |
        if grep -q 'build-backend = "poetry\.core\.masonry\.api"' "pyproject.toml"; then
          python -m pip install poetry
          poetry install
        else
          python -m pip install .
        fi

Then, with skip-install: false added:
https://github.com/ansys-internal/simba-core/pull/6/commits/191f76402b87d06257706c40c0129dbebc86011e

.github/workflows/ci_cd.yml

      - uses: ansys/actions/tests-pytest@d34d2c5cc77e0bfe0afcb6d913f38e0ad8c5f7bf
        with:
          pytest-extra-args: "--cov=ansys --cov-report=term --cov-report=html:.cov/html"
          skip-install: false

Then in https://github.com/ansys-internal/simba-core/actions/runs/8327598885/job/22785773885 poetry install is restored

...
Run if grep -q 'build-backend = "poetry\.core\.masonry\.api"' "pyproject.toml"; then
  if grep -q 'build-backend = "poetry\.core\.masonry\.api"' "pyproject.toml"; then
    python -m pip install poetry
    poetry install
  else
    python -m pip install .
  fi
...

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[anscfrisson]

https://github.com/ansys/actions/actions/runs/8331799321/job/22799487255?pr=427

Run ansys/actions/branch-name-style@main
Run branch_name=cfrisson/tests-pytests/inputs/add-skip-install
\033[[1](https://github.com/ansys/actions/actions/runs/8331799321/job/22799487255?pr=427#step:3:1);91m[ERROR]: Branch name cfrisson prefix is not valid.
Error: Process completed with exit code 1.

Re-opening new PR from renamed branch: #428