Set fixed ubuntu version for gh actions

.github/workflows/build.yml

@@ -16,7 +16,7 @@ on:
 jobs:
   build:
     name: Build and deploy docker images
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: Checkout
         uses: actions/checkout@v2

.github/workflows/codeql-analysis.yml

@@ -13,7 +13,7 @@ jobs:
   analyze:
     name: Analyze
     if: github.repository == 'photoview/photoview'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     strategy:
       fail-fast: false

.github/workflows/tests.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   test-api:
     name: Test API
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     defaults:
       run:
@@ -28,7 +28,7 @@ jobs:
       - name: Get C dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y build-essential libdlib-dev libblas-dev liblapack-dev libjpeg-turbo8-dev
+          sudo apt-get install -y libdlib-dev libblas-dev liblapack-dev libjpeg-turbo8-dev
 
       - name: Get GO dependencies
         run: |