Fix GPU runner targeting: use gpu-t4 for tests, gpu-v100 for docs

Both jobs segfaulted on demeter4 which has broken GPU drivers. Use
gpu-t4 (arctic1) for tests and gpu-v100 (demeter3, exclusive machine
with 2× V100-32GB) for the memory-hungry docs build.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

.github/workflows/GPU.yml

@@ -19,7 +19,7 @@ concurrency:
 jobs:
   gpu-tests:
     name: "GPU Tests"
-    runs-on: [self-hosted, Linux, X64, gpu]
+    runs-on: [self-hosted, Linux, X64, gpu-t4]
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@v6
@@ -39,8 +39,8 @@ jobs:
 
   gpu-docs:
     name: "Documentation"
-    runs-on: [self-hosted, Linux, X64, gpu]
-    timeout-minutes: 240
+    runs-on: [self-hosted, gpu-v100]
+    timeout-minutes: 360
     if: github.event_name == 'push' || !github.event.pull_request.draft
     steps:
       - uses: actions/checkout@v6