Use private endpoint runners (Infra) (#2364)

ci: use private endpoint runners

self-hosted testflinger runners are being deprecated in favor of centralized private endpoint runners

Author: pedro-avalos

.github/workflows/checkbox-promote-beta-to-candidate.yml

@@ -6,7 +6,7 @@ permissions:
 
 jobs:
   checkbox-promotion-beta-to-candidate-test:
-    runs-on: [self-hosted, testflinger]
+    runs-on: self-hosted-linux-amd64-jammy-private-endpoint-medium
     strategy:
       fail-fast: false
       matrix:

.github/workflows/dispatch_lab_job.yaml

@@ -24,7 +24,7 @@ on:
 
 jobs:
   run-matrix:
-    runs-on: [self-hosted, testflinger]
+    runs-on: self-hosted-linux-amd64-jammy-private-endpoint-medium
     strategy:
       fail-fast: false
       matrix:

.github/workflows/testflinger-contrib-dss-regression.yaml

@@ -49,7 +49,7 @@ jobs:
   regression-tests:
     needs: checkbox-dss-snap-build
     name: Tests
-    runs-on: [testflinger]
+    runs-on: self-hosted-linux-amd64-jammy-private-endpoint-medium
     defaults:
       run:
         working-directory: contrib/checkbox-dss-validation