Update brotli to 1.2.0 and python-urllib3 to 2.6.1.

In python-urllib3:

• Fixed a security issue where streaming API could improperly handle highly compressed HTTP content ("decompression bombs") leading to excessive resource consumption even when a small amount of data was requested. Reading small chunks of compressed data is safer and much more efficient now. (CVE-2025-66471 / `GHSA-2xpw-w6gg-jr37)
• Fixed a security issue where an attacker could compose an HTTP response with virtually unlimited links in the Content-Encoding header, potentially leading to a denial of service (DoS) attack by exhausting system resources during decoding. The number of allowed chained encodings is now limited to 5. (CVE-2025-66418 / `GHSA-gm62-xv2j-4w53)