[Merge] fix another error

.gitea/workflows/update-docs.yml

@@ -5,7 +5,7 @@ on:
       - 'docs/**'
 jobs:
   build_docs:
-    runs_on: ubuntu-latest
+    runs-on: ubuntu-latest
     steps:
       - name: Set up Git repository
         uses: actions/checkout@v6

src/core/math.sty

@@ -88,7 +88,6 @@
 \newcommand{\limsupni}{\limsup_{n \rightarrow \infty}}
 \newcommand{\sequence}[1]{(#1_n)_{n \geq 1}}
 \newcommand{\series}[2]{\sum_{k = 1}^{#2} #1_k}
-\newcommand{\elementstack}[2]{\genfrac{}{}{0pt}{}{#1}{#2}}
 
 \DeclareMathOperator\arctanh{arctanh}
 \DeclareMathOperator\arccosh{arccosh}