ci: run on Ubuntu 20.04

Author: JohelEGP

.github/workflows/check.yml

@@ -13,12 +13,12 @@ defaults:
 jobs:
   run-checks:
     name: Run checks
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
       - uses: actions/checkout@v2
       - name: install
-        run: sudo apt-get install latexmk texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended texlive-generic-recommended lmodern
+        run: sudo apt-get install latexmk texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended lmodern
       - name: make
         run: make quiet
       - name: check