maint: Add workflow_dispatch triggers to some CI Actions

Author: nickfloyd

.github/workflows/dotnetcore.yml

@@ -6,6 +6,7 @@ name: Build, test and publish
   pull_request:
     branches:
       - main
+  workflow_dispatch:
 env:
   config: Release
   PackageOutputPath: nupkg

.github/workflows/generate-schema.yml

@@ -8,6 +8,7 @@ name: Test Generate Schema
       - main
   schedule:
     - cron: 0 0 * * *
+  workflow_dispatch:
 jobs:
   build:
     runs-on: ubuntu-latest

.github/workflows/integration-tests.yml

@@ -3,6 +3,7 @@ name: Integration tests
   push: null
   schedule:
     - cron: 0 */24 * * *
+  workflow_dispatch:
   watch:
     types:
       - started