Update ModernisationPlatformSSOAdministrator role to include Sprinkler GitHub Actions role

[sukeshreddyg]

This PR updates the IAM policy for the ModernisationPlatformSSOAdministrator role. The new policy includes the Sprinkler GitHub Actions role as a valid principal that can assume this role (The update allows Sprinkler GitHub Actions to assume the ModernisationPlatformSSOAdministrator role)

[github-actions]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
❌ REPOSITORY	gitleaks	yes		2	0.66s
❌ REPOSITORY	trivy	yes		1	17.92s
⚠️ TERRAFORM	terraform-fmt	2		1	0.13s
✅ TERRAFORM	tflint	yes		no	9.62s

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