add manual CI trigger

Author: sdebruyn

.github/workflows/integration-tests-azure.yml

@@ -1,6 +1,7 @@
 ---
 name: Integration tests on Azure
 on:  # yamllint disable-line rule:truthy
+  workflow_dispatch:
   push:
     branches:
       - master

.github/workflows/integration-tests-sqlserver.yml

@@ -1,6 +1,7 @@
 ---
 name: Integration tests on SQL Server
 on:  # yamllint disable-line rule:truthy
+  workflow_dispatch:
   push:
     branches:
       - master

.github/workflows/unit-tests.yml

@@ -1,6 +1,7 @@
 ---
 name: Unit tests
 on:  # yamllint disable-line rule:truthy
+  workflow_dispatch:
   push:
     branches:
       - master