test_groups: route FMI + Initialization to GitHub-hosted runners (fix OOM kills)

The FMI and Initialization groups are memory-heavy and were getting OOM-killed
on the 4vcpu/8GB self-hosted runners that now back the `ubuntu-latest` label,
especially on `pre` (e.g. run 27742584454, jobs 82073267896 / 82073267635).

Designate `runner = "ubuntu-24.04"` for those groups (root + the
ModelingToolkitBase sublibrary's Initialization). GitHub-hosted ubuntu runners
have ~16GB (2x the 8GB self-hosted), and `ubuntu-24.04` deterministically
forces a GitHub-hosted runner because the self-hosted pool only carries the
`ubuntu-latest` label. Verified with compute_affected_sublibraries.jl
--root-matrix: FMI/Initialization now emit runner=ubuntu-24.04, all other
groups stay ubuntu-latest.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

lib/ModelingToolkitBase/test/test_groups.toml

@@ -10,6 +10,10 @@ versions = ["lts", "1", "pre"]
 
 [Initialization]
 versions = ["lts", "1", "pre"]
+# Memory-heavy (OOM-killed on the 4vcpu/8GB self-hosted runners, esp. on `pre`).
+# Route to a GitHub-hosted runner (~16GB). `ubuntu-24.04` forces GitHub-hosted
+# since the self-hosted pool only carries the `ubuntu-latest` label.
+runner = "ubuntu-24.04"
 
 [SymbolicIndexingInterface]
 versions = ["lts", "1", "pre"]

test/test_groups.toml

@@ -11,6 +11,10 @@ versions = ["lts", "1", "pre"]
 
 [Initialization]
 versions = ["lts", "1", "pre"]
+# Memory-heavy (OOM-killed on the 4vcpu/8GB self-hosted runners, esp. on `pre`).
+# Route to a GitHub-hosted runner (~16GB). `ubuntu-24.04` forces GitHub-hosted
+# since the self-hosted pool only carries the `ubuntu-latest` label.
+runner = "ubuntu-24.04"
 
 [SymbolicIndexingInterface]
 versions = ["lts", "1", "pre"]
@@ -26,6 +30,10 @@ versions = ["lts", "1", "pre"]
 
 [FMI]
 versions = ["lts", "1", "pre"]
+# Memory-heavy (OOM-killed on the 4vcpu/8GB self-hosted runners, esp. on `pre`).
+# Route to a GitHub-hosted runner (~16GB). `ubuntu-24.04` forces GitHub-hosted
+# since the self-hosted pool only carries the `ubuntu-latest` label.
+runner = "ubuntu-24.04"
 
 [QA]
 versions = ["lts", "1"]