gcc-changelog: add Unicode test-case

contrib/ChangeLog:

	* gcc-changelog/test_email.py: New test.
	* gcc-changelog/test_patches.txt: Likewise.

contrib/gcc-changelog/test_email.py

@@ -395,3 +395,7 @@ class TestGccChangelog(unittest.TestCase):
         err = email.errors[0]
         assert err.message == "pattern doesn't match any changed files"
         assert err.line == 'libstdc++-v3/testsuite/28_regex_not-existing/'
+
+    def test_unicode_chars_in_filename(self):
+        email = self.from_patch_glob('0001-Add-horse.patch')
+        assert not email.errors

contrib/gcc-changelog/test_patches.txt

@@ -3344,3 +3344,31 @@ index f51453f019a..d10ecf483f4 100644
 +
 --
 2.29.2
+
+=== 0001-Add-horse.patch ===
+From 2884248d07e4e2c922e137365253e2e521c425b0 Mon Sep 17 00:00:00 2001
+From: Martin Liska <mliska@suse.cz>
+Date: Mon, 21 Dec 2020 10:14:46 +0100
+Subject: [PATCH] Add horse.
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+ChangeLog:
+
+	* koníček.txt: New file.
+---
+ koníček.txt | 1 +
+ 1 file changed, 1 insertion(+)
+ create mode 100644 koníček.txt
+
+diff --git a/koníček.txt b/koníček.txt
+new file mode 100644
+index 00000000000..56c67f58752
+--- /dev/null
++++ b/koníček.txt
+@@ -0,0 +1 @@
++I'm a horse.
+-- 
+2.29.2
+