fix: molecule-tests matrix runner-index renders as empty for 0

scripts/ci/discover_runners.py

@@ -111,9 +111,14 @@ def get_runner_count(api_url: str, token: str, owner: str, repo: str) -> int:
     return DEFAULT_MAX_RUNNERS
 
 
-def generate_indices(count: int) -> list[int]:
-    """Generate a list of runner indices [0, 1, ..., count-1]."""
-    return list(range(count))
+def generate_indices(count: int) -> list[str]:
+    """Generate a list of runner indices ["0", "1", ..., "N-1"].
+
+    Uses strings instead of ints because Gitea Actions renders
+    integer 0 as empty in ${{ matrix.runner-index }} expressions,
+    causing --runner-index to be passed without a value.
+    """
+    return [str(i) for i in range(count)]
 
 
 @click.command()