[Aikido] Fix security issue in nokogiri via minor version upgrade from 1.18.10 to 1.19.3 in test

[aikido-autofix]

Upgrade Nokogiri to fix memory leak DoS, canonicalization signature bypass, and ReDoS vulnerabilities in CSS selectors.

✅ 3 CVEs resolved by this upgrade

This PR will resolve the following CVEs:

Issue	Severity	Description
GHSA-v2fc-qm4h-8hqv	LOW	[nokogiri] XSLT transform leaks small heap allocations when passed Ruby strings containing null bytes, potentially enabling denial of service attacks on long-running processes through sustained attacker-controlled input. Memory corruption and information disclosure do not occur.
GHSA-wx95-c6cv-8532	LOW	[nokogiri] Canonicalization failure in canonicalize methods returns empty string instead of raising an exception, allowing downstream libraries to accept invalid XML and bypass signature validation in SAML implementations.
GHSA-c4rq-3m3g-8wgx	LOW	[nokogiri] CSS selector tokenizer contains regular expressions vulnerable to ReDoS attacks on adversarial selectors, allowing attackers to cause exponential regex backtracking and denial of service through CSS parsing methods.

🔗 Related Tasks

• https://aikido.atlassian.net/browse/AIK-14274

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[aikido-autofix]

Closed by Aikido: a new AutoFix has been created → #293