fix(2): _load_meta whitelist UPGRADE_BASE_VERSION (override was silently dropped → base fell back to [-2])

The override added in a750937 had no effect: _load_meta only copies a fixed
key whitelist into the meta dict, and UPGRADE_BASE_VERSION wasn't in it, so
meta.get(...) returned None and the upgrade base fell back to previous_version()
= recipe_versions[-2] (0.6.3+3.1.2). Add it to the whitelist so discourse's
honest 0.7.0 base is selected.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

runner/run_recipe_ci.py

@@ -194,7 +194,7 @@ def _load_meta(recipe: str) -> dict:
         ns: dict = {}
         with open(path) as fh:
             exec(compile(fh.read(), path, "exec"), ns)  # noqa: S102 (trusted, in-repo)
-        for k in list(meta) + ["BACKUP_CAPABLE", "SKIP_GENERIC", "OIDC_AT_INSTALL", "READY_PROBE"]:
+        for k in list(meta) + ["BACKUP_CAPABLE", "SKIP_GENERIC", "OIDC_AT_INSTALL", "READY_PROBE", "UPGRADE_BASE_VERSION"]:
             if k in ns:
                 meta[k] = ns[k]
     return meta