Fix caching Gerrit account presence outside of repos

This fixes the case where a user tries to fetch new repos but isn't in
a Git directory (probably true for most people if they don't have,
e.g., their home directory as a Git repo).

There are a couple of ways to bikeshed a solution for this, but the
most straightforward/easiest is to skip since we're just caching the
account presence check.

Bug: b/328682976
Change-Id: I87a0b210451e6952839eef73616d012c41ad300f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6154836
Commit-Queue: Allen Li <ayatane@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>

gerrit_util.py

@@ -910,7 +910,18 @@ class GitCredsAuthenticator(_Authenticator):
             LOGGER.debug("Gerrit account does not exist on %r", host)
             return False
         LOGGER.debug("Gerrit account exists on %r", host)
-        scm.GIT.SetConfig(cwd, 'depot-tools.hostHasAccount', host, append=True)
+        try:
+            scm.GIT.SetConfig(cwd,
+                              'depot-tools.hostHasAccount',
+                              host,
+                              append=True)
+        except subprocess2.CalledProcessError as e:
+            # This may be called outside of a Git repository (e.g., when
+            # fetching from scratch), in which case we don't have a Git
+            # repository to cache the results of our check, so skip the
+            # caching.
+            LOGGER.debug(
+                "Got error trying to cache 'depot-tools.hostHasAccount': %s", e)
         return True
 
     def is_applicable(self, *, conn: Optional[HttpConn] = None):