ci: use gcc-10

.github/workflows/verible-ci.yml

diff --git a/.github/workflows/verible-ci.yml b/.github/workflows/verible-ci.yml
index 4aaee97..796abfa 100644
--- a/.github/workflows/verible-ci.yml
+++ b/.github/workflows/verible-ci.yml
@@ -154,9 +154,9 @@
       run: |
         set -x
         apt -qqy update
-        apt -qq -y install clang-10 build-essential wget git python3 python-is-python3
+        apt -qq -y install clang-10 build-essential wget git python3 python-is-python3 gcc-10 g++-10
         source ./.github/settings.sh
-        ./.github/bin/set-compiler.sh 9
+        ./.github/bin/set-compiler.sh 10
         ./.github/bin/install-bazel.sh
 
     - name: ${{ matrix.mode }} Verible