GHA: deprioritize Azure Ubuntu mirror

Due to year-long unreliability.

The default Ubuntu mirror works as fast as the Azure one when it's
working at its normal speed. And has HTTPS.

Also:
- replac the retry hack that turn out to not solve the problem.
- add timeouts to each download step to catch slowness early.

Follow-up to a5838847c4 #21181
Follow-up to 5172ba5475 #21107

Closes #21414

.github/workflows/non-native.yml

@@ -347,11 +347,10 @@ jobs:
       fail-fast: false
     steps:
       - name: 'install packages'
+        timeout-minutes: 2
         run: |
-          printf "#!/bin/sh
-            while [ \$? = 0 ]; do for i in 1 2 3; do timeout 30 \"\$@\" && break 2; echo \"Error: slow server, retry \$i\"; sleep 1
-            dpkg --configure -a; done; false; done" > "$HOME"/my-apt; chmod +x "$HOME"/my-apt
-          sudo "$HOME"/my-apt apt-get -o Dpkg::Use-Pty=0 install libfl2
+          sudo sed -i 's/priority:1/priority:9/' /etc/apt/apt-mirrors.txt; cat /etc/apt/apt-mirrors.txt
+          sudo apt-get -o Dpkg::Use-Pty=0 install libfl2
 
       - name: 'cache compiler (djgpp)'
         uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4