Only run GitHub Actions step if not a pull request - github-actions

Question

I have a workflow which needs to execute either on a push or a pull request with the exception of the last step which pushes a package to NuGet (I don't want this to occur on a pull request, even to master).
How can I prevent the Publish NuGet step from running if the workflow is triggered from a pull request?
name: .NET Core
on:
push:
branches: [ master ]
pull_request:
branches: [ master ]
jobs:
build:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout#v2
- name: Setup .NET Core
uses: actions/setup-dotnet#v1
with:
dotnet-version: 3.1.101
- name: Install dependencies
run: dotnet restore
- name: Build
run: dotnet build --configuration Release --no-restore
- name: Test
run: dotnet test --no-restore --verbosity normal
- name: Publish NuGet
uses: brandedoutcast/publish-nuget#v2.5.2
with:
PROJECT_FILE_PATH: "Orleans.Sagas/Orleans.Sagas.csproj"
NUGET_KEY: ${{secrets.NUGET_KEY}}

Answer 1

You can inspect the github.event_name context variable which contains the name of the event that triggered the workflow run. (eg, pull_request or push)
In this case, you can run a step for all events whose name is not pull_request with a github.event_name != 'pull_request' conditional on your step.
For example:
- name: Publish NuGet
uses: brandedoutcast/publish-nuget#v2.5.2
with:
PROJECT_FILE_PATH: "Orleans.Sagas/Orleans.Sagas.csproj"
NUGET_KEY: ${{secrets.NUGET_KEY}}
if: github.event_name != 'pull_request'

Answer 2

For future travellers, I found this action that worked quite well. I just needed to do an if: needs.pr-check.outputs.number != 'null' in order to filter by things being a PR or not.
https://github.com/8BitJonny/gh-get-current-pr
github.event_name != 'pull_request' did not work for me because the on.pull_request trigger doesn't exist for workflows that aren't launched by a PR.