Bump alpine to 3.21

Author: Gedochao

project/deps.sc

@@ -280,7 +280,7 @@ def buildCsM1Version = Deps.Versions.coursierM1Cli
 // Native library used to encrypt GitHub secrets
 def libsodiumVersion = "1.0.20"
 // Using the libsodium static library from this Alpine version (in the static launcher)
-def alpineVersion = "3.15"
+def alpineVersion = "3.21"
 
 object Docker {
   def customMuslBuilderImageName = "scala-cli-base-musl"