Move docs tests to custom runner (#3699)

# Description of Changes

<!-- Please describe your change, mention any related tickets, and so on
here. -->

Just moving more jobs to the custom runner.

|Test|Before|After|% Change|
|---|---|---|---|
|Docs - Build + Test|2m|1m|No change|
|Docs - Publish|2m|<2m|No change|

# API and ABI breaking changes

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corresponding GitHub label. -->

None

# Expected complexity level and risk

1 - This is very low risk

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# Testing

I ran a publish test and it worked just fine:
<https://github.com/clockworklabs/SpacetimeDB/actions/runs/19515454265/job/55865908554>

- [x] CI still passes

Co-authored-by: Zeke Foppa <bfops@users.noreply.github.com>

Author: jdetter

.github/workflows/docs-publish.yaml

@@ -10,7 +10,11 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: spacetimedb-new-runner
+    container:
+      image: localhost:5000/spacetimedb-ci:latest
+      options: >-
+        --privileged
     steps:
       - name: Checkout repository
         uses: actions/checkout@v3

.github/workflows/docs-test.yaml

@@ -7,7 +7,11 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: spacetimedb-new-runner
+    container:
+      image: localhost:5000/spacetimedb-ci:latest
+      options: >-
+        --privileged
     steps:
       - name: Checkout repository
         uses: actions/checkout@v3