[Aikido] Fix security issue in urllib3 via minor version upgrade from 2.5.0 to 2.6.3 in plausible-to-posthog

[aikido-autofix]

Upgrade urllib3 to mitigate critical decompression-based DoS vulnerabilities affecting streaming API and content encoding handling.

✅ Code not affected by breaking changes.

No breaking changes from the urllib3 upgrade affect this codebase. The codebase does not directly use urllib3 or any of the removed methods (HTTPResponse.getheaders(), HTTPResponse.getheader()), does not implement custom ContentDecoder classes, and does not handle Content-Encoding headers directly. While urllib3 is a transitive dependency, the code only uses higher-level libraries (posthog) that will handle any necessary compatibility updates internally.

All breaking changes by upgrading urllib3 from version 2.5.0 to 2.6.3 (CHANGELOG)

Version	Description
2.6.0	Removed the HTTPResponse.getheaders() method in favor of HTTPResponse.headers. Removed the HTTPResponse.getheader(name, default) method in favor of HTTPResponse.headers.get(name, default).
2.6.0	The number of allowed chained encodings in the Content-Encoding header is now limited to 5, which may cause responses with more than 5 chained encodings to fail.
2.6.0	The API of urllib3.response.ContentDecoder has changed, requiring custom decompressors to be updated.

✅ 3 CVEs resolved by this upgrade

This PR will resolve the following CVEs:

Issue	Severity	Description
CVE-2025-66418	HIGH	[urllib3] Decompression chain vulnerability allows attackers to cause excessive CPU and memory consumption by manipulating compression steps, potentially enabling a resource exhaustion denial-of-service (DoS) attack through maliciously crafted HTTP responses.
CVE-2025-66471	HIGH	[urllib3] A vulnerability in the streaming API allows attackers to cause excessive resource consumption by sending highly compressed HTTP responses, potentially leading to DoS through CPU and memory exhaustion.
CVE-2026-21441	HIGH	[urllib3] Vulnerability allows malicious servers to trigger excessive resource consumption via decompression bombs during HTTP redirects when streaming content, potentially causing DoS by exploiting content decoding before read methods are called.