Update GitHub Actions workflows to use ubuntu-20.04 for Python 3.5 compatibility

Co-authored-by: luzfcb <807599+luzfcb@users.noreply.github.com>

Author: Copilot

.github/workflows/build-test.yml

@@ -12,7 +12,7 @@ permissions:
 jobs:
   build:
     name: Build
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: Checkout do repositório
         uses: actions/checkout@v5

.github/workflows/github-pages.yml

@@ -15,7 +15,7 @@ concurrency:
 jobs:
   build:
     name: Build
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: Checkout do repositório
         uses: actions/checkout@v5
@@ -45,7 +45,7 @@ jobs:
     permissions:
       pages: write
       id-token: write
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}