Revert "GitHub Actions: Switch to GitHub-hosted runners"

This reverts commit 55e539d.

The recent switch to GitHub-hosted runners introduced issues with
actions/cache path handling, resulting in build failures due to
inconsistent home directory depths. Reverting to self-hosted runners to
restore build stability and functionality.

References:
- Issue: actions/cache#1440

Signed-off-by: Nikolay Martyanov <nikolay@zededa.com>

.github/workflows/build.yml

@@ -23,9 +23,9 @@ jobs:
         include:
           - os: buildjet-4vcpu-ubuntu-2204-arm
             arch: arm64
-          - os: ubuntu-20.04
+          - os: buildjet-4vcpu-ubuntu-2004
             arch: amd64
-          - os: ubuntu-20.04
+          - os: buildjet-4vcpu-ubuntu-2004
             arch: riscv64
     steps:
       - name: Starting Report
@@ -85,7 +85,7 @@ jobs:
 
   eve:
     needs: packages  # all packages for all platforms must be built first
-    runs-on: ubuntu-20.04
+    runs-on: buildjet-4vcpu-ubuntu-2004
     strategy:
       fail-fast: false
       matrix:

.github/workflows/buildondemand.yml

@@ -27,9 +27,9 @@ jobs:
         include:
           - os: buildjet-4vcpu-ubuntu-2204-arm
             arch: arm64
-          - os: ubuntu-20.04
+          - os: buildjet-4vcpu-ubuntu-2004
             arch: amd64
-          - os: ubuntu-20.04
+          - os: buildjet-4vcpu-ubuntu-2004
             arch: riscv64
     steps:
       - name: Starting Report
@@ -83,7 +83,7 @@ jobs:
     needs: packages  # all packages for all platforms must be built first
     # Only run for the default branch
     if: github.ref_name == github.event.repository.default_branch
-    runs-on: ubuntu-20.04
+    runs-on: buildjet-4vcpu-ubuntu-2004
     strategy:
       fail-fast: false
       matrix: