Fix source tag branch segment to main (per review)

Reviewer specified the onboarding-funnel source tag as <repo>:main:v1.0 -- the
middle segment is the branch the sample lives on (main), not the 'sample-sdk' label.

Author: saraswati-padmawar

NunitCsharpReqnrollPlaywrightBrowserstack.Tests/browserstack.yml

@@ -27,7 +27,7 @@ buildIdentifier: '#${BUILD_NUMBER}' # Supports strings along with either/both ${
 # Reqnroll (BDD layer) is auto-detected by the SDK on top of the runner declared here.
 framework: nunit
 
-source: nunit-csharp-reqnroll-playwright-browserstack:sample-sdk:v1.0
+source: nunit-csharp-reqnroll-playwright-browserstack:main:v1.0
 
 # =======================================
 # Platforms (Browsers / Devices to test)