sdl12-compat: Install GLU development headers for the linux-verify step

SDL Commits
1 
From 49be0d7522a49dd76b7c51864b4fbfcab2fc67ea Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Tue, 2 Dec 2025 12:09:18 -0800
Subject: [PATCH] Install GLU development headers for the linux-verify step

---
 .github/workflows/release.yml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 14e1d239c..c3d86d6fc 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -110,6 +110,10 @@ jobs:
           install-linux-dependencies: true
       - name: Set up ninja
         uses: ./.github/actions/setup-ninja
+      - name: Install GLU development headers
+        run: |
+          sudo apt update -q
+          sudo apt install -y libgl1-mesa-dev libglu1-mesa-dev
       - name: 'CMake (configure + build)'
         run: |
           cmake \