docs: derive current_version from DOCS_DISPLAY_VERSION too

The previous fix set only display_version from DOCS_DISPLAY_VERSION, but the
version switcher (current_version and generateVersionsDocs) still relied on
_stable_ver, which is empty in the consolidated deploy — so the switcher showed
"latest" and highlighted the wrong version. Let _stable_ver honour
DOCS_DISPLAY_VERSION so all three resolve to the built version.

Assisted-by: ClaudeCode:claude-opus-4-8
Signed-off-by: skjnldsv <skjnldsv@protonmail.com>

Author: skjnldsv

conf.py

@@ -66,12 +66,15 @@
 version_stable = 34		# mapped to https://docs.nextcloud.com/server/stable/
 import re as _re
 # Detect stable branch version for display purposes.
+# In the consolidated deploy DOCS_DISPLAY_VERSION carries the built version (the
+# reserved GITHUB_* refs cannot be set per matrix leg).
 # For PRs: GITHUB_BASE_REF is the target branch (e.g. 'stable34').
 # For direct pushes: GITHUB_REF is 'refs/heads/stable34'.
 _base = os.environ.get('GITHUB_BASE_REF', '')
 _ref  = os.environ.get('GITHUB_REF', '')
 _stable_ver = (
-    _re.match(r'^stable(\d+)$', _base)
+    _re.match(r'^(\d+)$', os.environ.get('DOCS_DISPLAY_VERSION', ''))
+    or _re.match(r'^stable(\d+)$', _base)
     or _re.match(r'^refs/heads/stable(\d+)$', _ref)
 )
 display_version = (