gitlab-ci: use eatmydata in apt-get

apt-get uses several fsync() calls on each package it installs, and that's
very slow, especially on non-SSD. eatmydata turns fsync into no-op, which
makes package installation much faster (it can cause corruption if there's
power loss or similar, but that doesn't matter in CI where we throw away
the whole container anyway).

Currently the build_ubuntu_20_04 job in GitLab CI takes 8-9 minutes to
install dependencies. Using eatmydata it went down to 2 minutes.

.gitlab-ci.yml

@@ -13,8 +13,9 @@ build_ubuntu_20_04:
   before_script:
     - sed -i -e 's/# deb-src/deb-src/g' /etc/apt/sources.list
     - apt-get update
-    - apt-get build-dep --yes --no-install-recommends okular
+    - apt-get install --yes eatmydata
-    - apt-get install --yes --no-install-recommends ninja-build
+    - eatmydata apt-get build-dep --yes --no-install-recommends okular
+    - eatmydata apt-get install --yes --no-install-recommends ninja-build
   script:
     - mkdir -p build && cd build
     - cmake -DOKULAR_UI=desktop -G Ninja ..
@@ -31,8 +32,9 @@ build_clazy_clang_tidy:
   before_script:
     - echo 'deb-src http://deb.debian.org/debian unstable main' >> /etc/apt/sources.list
     - apt-get update
-    - apt-get build-dep --yes --no-install-recommends okular
+    - apt-get install --yes eatmydata
-    - apt-get install --yes --no-install-recommends ninja-build clazy clang clang-tidy libkf5crash-dev libkf5purpose-dev libegl-dev jq
+    - eatmydata apt-get build-dep --yes --no-install-recommends okular
+    - eatmydata apt-get install --yes --no-install-recommends ninja-build clazy clang clang-tidy libkf5crash-dev libkf5purpose-dev libegl-dev jq
 
   script:
     - srcdir=`pwd` && mkdir -p /tmp/okular_build && cd /tmp/okular_build && CC=clang CXX=clazy CXXFLAGS="-Werror -Wno-deprecated-declarations" cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -G Ninja $srcdir && cat compile_commands.json | jq  '[.[] | select(.file | contains("'"$srcdir"'"))]' > compile_commands.aux.json && cat compile_commands.aux.json | jq  '[.[] | select(.file | contains("/synctex/")| not)]' > compile_commands.json && cp "$srcdir/.clang-tidy" .