Run tests in CI (Windows OS only for now)

The reason for such a hack when runing in CI is because we
need to make sure we're using higher sequence numbers than
any previous times (and even previous runs of the test suite).

And we run 1 test only for now, later we will enable more.

Other notes:

The trick to extract secrets to files was taken from:
https://stackoverflow.com/a/59482124/544947

The binary-to-text encoding/decoding was taken from:
https://stackoverflow.com/a/42725926/544947

The way to add defines to DefineConstants for MSBuild:
https://stackoverflow.com/a/5053070/544947

.github/workflows/CI.yml

@@ -47,4 +47,23 @@ jobs:
       uses: microsoft/setup-msbuild@v1
 
     - name: Build Project
-      run: MSBuild src/TgSharp.sln
+      run: MSBuild src/TgSharp.sln && MSBuild -t:Clean src/TgSharp.sln
+
+    - name: Prepare test suite assets
+      run: |
+        echo "$APP_CONFIG_IN_TESTS" > app.config
+        echo "$SESSION_DAT_IN_TESTS" > encodedSession.dat
+      shell: bash
+      env:
+        APP_CONFIG_IN_TESTS: ${{secrets.APP_CONFIG_IN_TESTS}}
+        SESSION_DAT_IN_TESTS: ${{secrets.SESSION_DAT_IN_TESTS}}
+
+    - name: Run Tests
+      run: |
+        MSBuild -p:Configuration=Debug -p:CI=true src/TgSharp.sln
+
+        certutil -decode encodedSession.dat src/TgSharp.Tests.NUnit/bin/Debug/session.dat
+        cp app.config src/TgSharp.Tests.NUnit/bin/Debug/TgSharp.Tests.NUnit.dll.config
+
+        ./Nuget.exe install NUnit.Runners -Version 3.11.1 -OutputDirectory packages
+        ./packages/NUnit.ConsoleRunner.3.11.1/tools/nunit3-console.exe src/TgSharp.Tests.NUnit/bin/Debug/TgSharp.Tests.NUnit.dll