exttst: Pass encoding to InputStreamReader

errorprone was complaining about this lack of encoding in the test.

Change-Id: I53916a3e3446d965a77393b6705fb86ecff0d931
diff --git a/org.eclipse.jgit.test/exttst/org/eclipse/jgit/ignore/CGitVsJGitRandomIgnorePatternTest.java b/org.eclipse.jgit.test/exttst/org/eclipse/jgit/ignore/CGitVsJGitRandomIgnorePatternTest.java
index 23a267c..47a410b 100644
--- a/org.eclipse.jgit.test/exttst/org/eclipse/jgit/ignore/CGitVsJGitRandomIgnorePatternTest.java
+++ b/org.eclipse.jgit.test/exttst/org/eclipse/jgit/ignore/CGitVsJGitRandomIgnorePatternTest.java
@@ -164,7 +164,7 @@ private Process startCgitCheckIgnore(String path) throws IOException {
 		private String readProcessStream(InputStream processStream)
 				throws IOException {
 			try (BufferedReader stdOut = new BufferedReader(
-					new InputStreamReader(processStream))) {
+					new InputStreamReader(processStream, UTF_8))) {
 
 				StringBuilder out = new StringBuilder();
 				String s;