[PATCH] ci: add job for gcc-4.8 to GitHub Actions

["Carlo Marcelo Arenas Belón" <carenas@gmail.com>]

unlike the other jobs; using an older ubuntu base image that provides
that compiler as an option.

note the obsoleted travis job used an image of the OS that is EOL and
therefore not available, but the compiler used will be the same, and
more importantly will fail in the same (C89 compatibility) issues.

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
---
based on top of my tip for cb/reftable-fixes, but applies cleanly all
the way to maint.

a succesful run can be seen in:

  https://github.com/carenas/git/runs/3336674183

it adds 2m to the current setup, but gcc 4.8 is hard to find in modern
developer workstations (or even non EOL enterprise systems)

 .github/workflows/main.yml | 3 +++
 ci/install-dependencies.sh | 6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 73856bafc9..0f211173fc 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -297,6 +297,9 @@ jobs:
           - jobname: linux-gcc-default
             cc: gcc
             pool: ubuntu-latest
+          - jobname: linux-gcc-4.8
+            cc: gcc-4.8
+            pool: ubuntu-18.04
     env:
       CC: ${{matrix.vector.cc}}
       jobname: ${{matrix.vector.jobname}}
diff --git a/ci/install-dependencies.sh b/ci/install-dependencies.sh
index 67852d0d37..950bc39129 100755
--- a/ci/install-dependencies.sh
+++ b/ci/install-dependencies.sh
@@ -72,10 +72,14 @@ Documentation)
 	test -n "$ALREADY_HAVE_ASCIIDOCTOR" ||
 	sudo gem install --version 1.5.8 asciidoctor
 	;;
-linux-gcc-default|linux-gcc-4.8)
+linux-gcc-default)
 	sudo apt-get -q update
 	sudo apt-get -q -y install $UBUNTU_COMMON_PKGS
 	;;
+linux-gcc-4.8)
+	sudo apt-get -q update
+	sudo apt-get -q -y install $UBUNTU_COMMON_PKGS gcc-4.8
+	;;
 esac
 
 if type p4d >/dev/null && type p4 >/dev/null
-- 
2.33.0.rc2.476.g1b09a32a73