ci: harden coverage omit so config-3.py phantom never trips xml

The bare "config-3.py" omit never matched the phantom's absolute path
(D:\a\...\config-3.py), so coverage xml only survived via --ignore-errors
and still logged the alarming "No source for code" line. Use a glob
(*config-*.py) that matches the phantom at any path while keeping
src/config.py measured (verified via coverage GlobMatcher).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.coveragerc

@@ -2,9 +2,11 @@
 [run]
 branch = True
 source = src
-# Exclude conda internal shims that leak into coverage data
+# Exclude conda/xonsh internal shims that leak into coverage data. The phantom
+# is an absolute path like D:\a\...\config-3.py, so a bare "config-3.py" omit
+# never matches — use a glob that matches any path ending in config-<n>.py.
 omit =
-    config-3.py
+    *config-*.py
     */site-packages/*
     */conda-meta/*