Auto merge of #74163 - cuviper:debian6, r=Mark-Simulacrum

Auto merge of #74163 - cuviper:debian6, r=Mark-Simulacrum

ci: Update dist-{i686,x86_64}-linux to Debian 6

This increases the minimum `{i686,x86_64}-unknown-linux-gnu` platform
from RHEL/CentOS 5 (glibc 2.5 and kernel 2.6.18) to a slightly newer
Debian 6 `squeeze` (glibc 2.11 and kernel 2.6.32). While that release is
already EOL, it happens to match the minimum common versions of two
enterprise distros that do still need Rust support -- RHEL 6 (glibc 2.12
and kernel 2.6.32) and SLES 11 SP4 (glibc 2.11 and kernel 3.0).

Closes #62516.