Preinstall curl before integration testing

Author: m-dzianishchyts

jjava-distro/src/test/java/org/dflib/jjava/distro/ContainerizedKernelCase.java

@@ -100,7 +100,7 @@ private static void initializeContainer() {
     private static String getStartupCommand() {
         return String.join(" && ",
                 "apt-get update",
-                "apt-get install --no-install-recommends -y python3 python3-pip python3-venv",
+                "apt-get install --no-install-recommends -y python3 python3-pip python3-venv curl",
                 "python3 -m venv ./venv",
                 venvCommand("pip install jupyter-console --progress-bar off"),
                 "tail -f /dev/null"

jjava-distro/src/test/java/org/dflib/jjava/distro/KernelMagicIT.java

@@ -19,7 +19,7 @@ public void jars() throws Exception {
                 "https://repo1.maven.org/maven2/jakarta/annotation/jakarta.annotation-api/3.0.0/jakarta.annotation-api-3.0.0.jar",
                 "-o", jar
         );
-        assertEquals("", fetchResult.getStderr());
+        assertEquals(0, fetchResult.getExitCode(), fetchResult.getStdout() + "\n" + fetchResult.getStderr());
 
         String snippet = String.join("\n",
                 "%jars " + jar,