Fix syntax error in isValidEmail method

[devin-ai-integration]

Fix syntax error in isValidEmail method and update deprecated GitHub Actions

Summary

This PR addresses a CI build failure that had two root causes:

1. Syntax error: Missing semicolon in the new isValidEmail method in Util.java
2. Deprecated dependencies: GitHub Actions workflow was using v2 actions that have been shut down by GitHub

The changes include:

• Fixed compilation error by adding missing semicolon to isValidEmail method
• Added basic email validation logic that checks for non-null input and presence of "@" symbol
• Updated GitHub Actions workflow to use current stable versions (checkout@v5, setup-java@v5, cache@v4)

Review & Testing Checklist for Human

• Verify email validation requirements - The current implementation only checks for != null && contains("@"). Confirm this basic validation meets your requirements, as it would accept strings like "@@", "a@", or "@b" as valid emails
• Consider adding unit tests - The new isValidEmail method has no test coverage. Should we add tests to verify the validation behavior?
• Test CI workflow - Verify the updated GitHub Actions versions work correctly and don't introduce any unexpected behavior changes

Notes

• All 68 existing tests continue to pass
• The isValidEmail method is not yet used anywhere in the codebase
• GitHub deprecated actions/cache@v2 in December 2024, requiring the workflow updates

Link to Devin run: https://app.devin.ai/sessions/981a350c109f4b4c83d56eec4eeb7802
Requested by: @samfert-codeium

[devin-ai-integration]

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