Condense FetchInfo.refresh using contextlib.suppress

I think this refactoring slightly improves readability.

+ Condense/sort/group imports (while adding contextlib import).

+ Minor style tweaks in FetchInfo.refresh comments.

+ Make a comment in Git.refresh clearer, building on revisions in:
  #1810 (comment)

git/cmd.py

@@ -478,7 +478,7 @@ def refresh(cls, path: Union[None, PathLike] = None) -> bool:
                 # We get here if this was the initial refresh and the refresh mode was
                 # not error. Go ahead and set the GIT_PYTHON_GIT_EXECUTABLE such that we
                 # discern the difference between the first refresh at import time
-                # and subsequent calls to refresh().
+                # and subsequent calls to git.refresh or this refresh method.
                 cls.GIT_PYTHON_GIT_EXECUTABLE = cls.git_exec_name
             else:
                 # After the first refresh (when GIT_PYTHON_GIT_EXECUTABLE is no longer

git/remote.py

@@ -5,30 +5,24 @@
 
 """Module implementing a remote object allowing easy access to git remotes."""
 
+import contextlib
 import logging
 import re
 
-from git.cmd import handle_process_output, Git
+from git.cmd import Git, handle_process_output
 from git.compat import defenc, force_text
+from git.config import GitConfigParser, SectionConstraint, cp
 from git.exc import GitCommandError
+from git.refs import Head, Reference, RemoteReference, SymbolicReference, TagReference
 from git.util import (
-    LazyMixin,
-    IterableObj,
+    CallableRemoteProgress,
     IterableList,
+    IterableObj,
+    LazyMixin,
     RemoteProgress,
-    CallableRemoteProgress,
-)
-from git.util import (
     join_path,
 )
 
-from git.config import (
-    GitConfigParser,
-    SectionConstraint,
-    cp,
-)
-from git.refs import Head, Reference, RemoteReference, SymbolicReference, TagReference
-
 # typing-------------------------------------------------------
 
 from typing import (
@@ -345,18 +339,13 @@ class FetchInfo(IterableObj):
     @classmethod
     def refresh(cls) -> Literal[True]:
         """This gets called by the refresh function (see the top level __init__)."""
-        # clear the old values in _flag_map
-        try:
+        # Clear the old values in _flag_map.
+        with contextlib.suppress(KeyError):
             del cls._flag_map["t"]
-        except KeyError:
-            pass
-
-        try:
+        with contextlib.suppress(KeyError):
             del cls._flag_map["-"]
-        except KeyError:
-            pass
 
-        # set the value given the git version
+        # Set the value given the git version.
         if Git().version_info[:2] >= (2, 10):
             cls._flag_map["t"] = cls.TAG_UPDATE
         else: