tests: Fix makeNewRelease when installed as a zipped egg

python ZipFile module does not support updating an entry in place, instead make
a new zip file and copy all entries.

src/zc/buildout/tests.py

@@ -3462,16 +3462,18 @@ def makeNewRelease(project, ws, dest, version='99.99'):
         ).groups()
     dest = os.path.join(dest, "%s-%s-py%s.egg" % (eggname, version, pyver))
     if os.path.isfile(dist.location):
-        shutil.copy(dist.location, dest)
-        zip = zipfile.ZipFile(dest, 'a')
-        zip.writestr(
-            'EGG-INFO/PKG-INFO',
-            ((zip.read('EGG-INFO/PKG-INFO').decode('ISO-8859-1')
-              ).replace("Version: %s" % oldver,
-                        "Version: %s" % version)
-             ).encode('ISO-8859-1')
-            )
-        zip.close()
+        with zipfile.ZipFile(dist.location, 'r') as old_zip:
+            with zipfile.ZipFile(dest, 'w') as new_zip:
+                for item in old_zip.infolist():
+                    data = old_zip.read(item.filename)
+                    if item.filename == 'EGG-INFO/PKG-INFO':
+                        data = data.decode(
+                            'ISO-8859-1'
+                          ).replace(
+                            "Version: %s" % oldver,
+                            "Version: %s" % version
+                          ).encode('ISO-8859-1')
+                    new_zip.writestr(item, data)
     else:
         shutil.copytree(dist.location, dest)
         info_path = os.path.join(dest, 'EGG-INFO', 'PKG-INFO')