ci: raise the three 55m unit shards to the 60m job-timeout invariant

`check_workflow_startup_safety.py` requires a unit shard's job timeout to
cover the pytest budget plus the setup ceiling plus runner overhead:
20 + 35 + 5 = 60. Three shards in test-unit.yml — caching-local,
proxy-extras and enterprise-package — capped the job at 55m, so the job
deadline could preempt pytest while the checks list stayed green. The
other ten shards already use 60.

This is why `code-quality` has been failing on every PR against
litellm_internal_staging, including ones that touch no workflow files.

Raise the three to 60. The checker now reports "Workflow startup
invariants hold (setup ceiling 35m)".

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/test-unit.yml

@@ -211,7 +211,7 @@ jobs:
             workers: 2
             reruns: 2
             timeout-minutes: 20
-            job-timeout-minutes: 55
+            job-timeout-minutes: 60
 
           - shard: proxy-extras
             artifact-name: proxy-extras
@@ -219,7 +219,7 @@ jobs:
             workers: 2
             reruns: 2
             timeout-minutes: 20
-            job-timeout-minutes: 55
+            job-timeout-minutes: 60
 
           - shard: enterprise-package
             artifact-name: enterprise-package
@@ -227,7 +227,7 @@ jobs:
             workers: 4
             reruns: 2
             timeout-minutes: 20
-            job-timeout-minutes: 55
+            job-timeout-minutes: 60
 
           - shard: responses-caching-types
             artifact-name: responses-caching-types