fix: Image broken in default slack notification template

[SATYAsasini]

Description

Fixes #5607

Checklist:

• The title of the PR states what changed and the related issues number (used for the release note).
• Does this PR requires documentation updates?
• I've updated documentation as required by this PR.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have tested it for all user roles.
• I have added all the required unit/api test cases.

Does this PR introduce a user-facing change?

[gitguardian]

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[sonarqubecloud]

Quality Gate failed

Failed conditions
97.8% Duplication on New Code (required ≤ 3%)

See analysis details on SonarCloud