CLSA-2026-1777626401 python3: Fix of 3 CVEs

CVE-2026-6100: clear dangling nextin pointer on MemoryError in bz2/lzma decompressors to avoid use-after-free on instance reuse - CVE-2026-4786: validate the post-substitution URL in webbrowser UnixBrowser.open so that "%action" cannot smuggle a dash-prefixed flag past the CVE-2026-4519...