installdependencies.sh: add fallback to libssl-dev / libicu-dev for Debian 14+

Describe the bug

src/Misc/layoutbin/installdependencies.sh uses hardcoded, versioned package names for OpenSSL and ICU libraries:

• OpenSSL: tries libssl3t64$ → libssl3$ → libssl1.1$ → libssl1.0.2$ → libssl1.0.0$ (line 105)
• ICU: tries libicu80 → libicu79 → … → libicu52 (line 113)

On Debian 14 (and potentially other newer distributions), none of these versioned packages may exist. The script has no fallback to the unversioned development packages (libssl-dev, libicu-dev) which are available on these systems.

When all fallbacks are exhausted, the script exits with:

Can't install dotnet core dependencies.

This blocks self-hosted runner setup on Debian 14.

To Reproduce

1. Set up a Debian 14 (or newer) system.
2. Run sudo ./src/Misc/layoutbin/installdependencies.sh
3. Observe failure — none of the versioned libssl* or libicu* packages can be found by apt-get.

Expected behavior

The script should fall back to the development packages (libssl-dev, libicu-dev) when none of the versioned runtime packages are available. The -dev packages are the canonical unversioned names and are available across all Debian/Ubuntu versions.

Alternatively (or additionally), the script could use apt-cache search / apt list to dynamically discover the available library package names at runtime instead of maintaining a hardcoded list.

Proposed Fix

In the Debian-based branch (after line 69), add a final fallback that tries the -dev packages before failing:

# After the existing fallback chain fails, try -dev packages
apt_get_with_fallbacks libssl-dev
if [ $? -ne 0 ]; then
    echo "'$apt_get' failed to install libssl"
    print_errormessage
    exit 1
fi

apt_get_with_fallbacks libicu-dev
if [ $? -ne 0 ]; then
    echo "'$apt_get' failed to install libicu"
    print_errormessage
    exit 1
fi

A more robust approach would be to query available packages dynamically:

# Find available libssl package
SSL_PKG=$(apt-cache search '^libssl[0-9]' | head -1 | cut -d' ' -f1)
if [ -n "$SSL_PKG" ]; then
    $apt_get install -y "$SSL_PKG"
fi

Runner Version and Platform

• Version of runner: latest (main branch, commit c814d7ca)
• OS: Debian 14 (and any future Debian/Ubuntu versions where versioned so-names change)

What's not working?

The installdependencies.sh script cannot install required .NET dependencies on Debian 14 because:

Package type	Hardcoded names in script	Available on Debian 14
OpenSSL	libssl3t64, libssl3, libssl1.1, libssl1.0.2, libssl1.0.0	libssl-dev
ICU	libicu80 … libicu52	libicu-dev (or libicu74 etc.)

Additional context

• The Debian-based branch starts at line 45 of the script.
• The apt_get_with_fallbacks function (line 77–95) tries each argument in order but gives up if none succeeds.
• This pattern has the same maintenance burden as the ICU version list — each new Debian/Ubuntu release may introduce a new soname and break the script again.
• Using the -dev packages as a final fallback avoids this maintenance treadmill.

Start with src/Misc/layoutbin/installdependencies.sh, reading the Debian-based branch and the apt_get_with_fallbacks function around the mentioned lines. Reproduce the dependency installation on Debian 14, then verify that the final fallback handles libssl-dev and libicu-dev and that the script completes successfully.