Update use of inputs.install-package variable

[hannahilea]

Setting

      - uses: julia-actions/julia-docdeploy@v1
        with:
          install-package: false

as in the docs doesn't actually cause the relevant run step to be skipped in

julia-docdeploy/action.yml

Line 39 in 80c0bdc

if: ${{ inputs.install-package }}

I suspect this is related to actions/runner#1483, hence the proposed change.

[SaschaMann]

Thanks!

[hannahilea]

Thanks for responding to this so quickly!