bpo-43651: PEP 597: Fix EncodingWarning in some tests (GH-25171)

* Fix test_float
* Fix _osx_support
* Fix test_fstring
* Fix test_gc
* Fix test_gzip
* Fix test_hashlib
* Fix unrelated whitespace issue

Co-authored-by: Ned Deily <nad@python.org>
diff --git a/Lib/test/test_hashlib.py b/Lib/test/test_hashlib.py
index f50a455..0e06fdc 100644
--- a/Lib/test/test_hashlib.py
+++ b/Lib/test/test_hashlib.py
@@ -82,7 +82,7 @@ def hexstr(s):
 def read_vectors(hash_name):
     url = URL.format(hash_name)
     try:
-        testdata = support.open_urlresource(url)
+        testdata = support.open_urlresource(url, encoding="utf-8")
     except (OSError, HTTPException):
         raise unittest.SkipTest("Could not retrieve {}".format(url))
     with testdata: