Fixes Debian 11 compat

Fixes sbt#7118

Problem
-------
sbtn 1.8.1 was built using ubuntu-latest, which meant picking up newer
glibc.

Solution
--------
This downgraded the ubuntu machine to build sbtn.

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             java: 17
             distribution: temurin
             jobtype: 1

launcher-package/build.sbt

@@ -121,7 +121,7 @@ val root = (project in file(".")).
       file
     },
     // update sbt.sh at root
-    sbtnVersion := "1.8.1",
+    sbtnVersion := "1.8.2",
     sbtnJarsBaseUrl := "https://github.com/sbt/sbtn-dist/releases/download",
     sbtnJarsMappings := {
       val baseUrl = sbtnJarsBaseUrl.value

main/src/test/scala/sbt/internal/InstallSbtnSpec.scala

@@ -37,7 +37,7 @@ class InstallSbtnSpec extends AnyFlatSpec {
   "InstallSbtn" should "extract native sbtn" ignore
     withTemp(".zip") { tmp =>
       withTemp(".exe") { sbtn =>
-        InstallSbtn.extractSbtn(term, "1.8.1", tmp, sbtn)
+        InstallSbtn.extractSbtn(term, "1.8.2", tmp, sbtn)
         val tmpDir = Files.createTempDirectory("sbtn-test").toRealPath()
         Files.createDirectories(tmpDir.resolve("project"))
         val foo = tmpDir.resolve("foo")

sbt

@@ -24,7 +24,7 @@ declare build_props_sbt_version=
 declare use_sbtn=
 declare no_server=
 declare sbtn_command="$SBTN_CMD"
-declare sbtn_version="1.8.1"
+declare sbtn_version="1.8.2"
 
 ###  ------------------------------- ###
 ###  Helper methods for BASH scripts ###