ci: update libtinfo5 installation for Ubuntu 24.04

As per actions/runner-images#10636
`ubuntu-latest` is now Ubuntu 24.04 instead of 22.04 which [does not]
have `libtinfo5` in the default PPAs

[does not]: https://packages.ubuntu.com/search?keywords=libtinfo

Unfortunately all of the LLVM binary releases still for Ubuntu still
target 18.04 and contain binaries linked against `libtinfo5` — bumping
the version of LLVM we use in our tests' toolchains will not solve this
problem.

Pinning CI to use Ubuntu 22.04 is an option; however this PR installs
`libtinfo5` on the Ubuntu 24.04 runners manually instead.

.github/workflows/tests.yml

@@ -33,8 +33,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - if: startsWith(matrix.os, 'ubuntu')
-        name: Install APT packages
-        run: sudo apt-get -y install libtinfo5
+        run: tests/scripts/ubuntu_install_libtinfo.sh
       - uses: actions/checkout@v4
       - name: Test
         env:
@@ -52,8 +51,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - if: startsWith(matrix.os, 'ubuntu')
-        name: Install APT packages
-        run: sudo apt-get -y install libtinfo5
+        run: tests/scripts/ubuntu_install_libtinfo.sh
       - uses: actions/checkout@v4
       - name: Test
         env:
@@ -102,8 +100,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: ubuntu-latest
     steps:
-      - name: Install APT packages
-        run: sudo apt-get -y install libtinfo5
+      - run: tests/scripts/ubuntu_install_libtinfo.sh
       - uses: actions/checkout@v4
       - name: Test
         env:
@@ -116,8 +113,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: ubuntu-latest
     steps:
-      - name: Install APT packages
-        run: sudo apt-get -y install libtinfo5
+      - run: tests/scripts/ubuntu_install_libtinfo.sh
       - uses: actions/checkout@v4
       - name: Download and Extract LLVM distribution
         env:

tests/scripts/ubuntu_install_libtinfo.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+# Ubuntu 24.04 does not have libtinfo5 in its PPAs:
+#
+# However, the LLVM binary releases hosted up upstream still target Ubuntu 18.04
+# as of this writing and contain binaries linked against `libtinfo5`.
+#
+# This script installs `libtinfo5` using the `.deb` from Ubuntu 22.04's PPAs:
+# https://packages.ubuntu.com/jammy-updates/amd64/libtinfo5/download
+
+set -euo pipefail
+
+readonly pkg="$(mktemp --suffix=.deb)"
+trap EXIT 'rm -f "$pkg"'
+
+curl -L https://mirrors.kernel.org/ubuntu/pool/universe/n/ncurses/libtinfo5_6.3-2ubuntu0.1_amd64.deb -o "$pkg"
+dpkg -i "$pkg"
+