ci(bump): gate toolchain install behind a cheap version check; fix binpkg verify

The daily Bump job emerged a full Go/pkgdev toolchain (and synced ::gentoo,
~5-26 min) on every run before bump-version.sh checked whether anything was
actually out of date — which, on the common no-op day, it isn't. Add a cheap
first step that compares the newest upstream release (releases.rss) against the
newest committed ebuild (Gitea contents API) using only base-image wget, and
gate the sync/install/bump steps on its `needed` output. The gate only
short-circuits when confident both versions parsed and current >= upstream;
on any doubt it falls through to the full run, where bump-version.sh remains
the source of truth.

Also fix the binpkg signature-verification disable in both workflows: the
`sed 's/^verify-signature = true/.../'` matched nothing in the stage3 binhost
config, so every emerge flooded the log with GPG failures ("unknown key",
missing pubring.kbx, "Try running getuto"). Delete any verify-signature line
and append `verify-signature = false` so the knob is actually set.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018MsAYv5RhNLE54fPrviVgS

.gitea/workflows/ci.yaml

@@ -22,8 +22,8 @@ jobs:
           mkdir -p /etc/portage/repos.conf
           printf '[DEFAULT]\nmain-repo = gentoo\n\n[gentoo]\nlocation = /var/db/repos/gentoo\n' \
             > /etc/portage/repos.conf/gentoo.conf
-          sed -i 's/^verify-signature = true/verify-signature = false/' \
-            /etc/portage/binrepos.conf/gentoo.conf
+          sed -i '/^verify-signature/d' /etc/portage/binrepos.conf/gentoo.conf
+          printf '\nverify-signature = false\n' >> /etc/portage/binrepos.conf/gentoo.conf
           emerge -q --getbinpkg net-misc/curl dev-util/pkgcheck
 
       # Place this overlay at /var/db/repos/azy5030. actions/checkout is avoided