filter-repo: improve invalid repository error message

Even though the repository is encoded as a bytestring, we want error
messages to be UTF-8.

Signed-off-by: Elijah Newren <newren@gmail.com>

git-filter-repo

@@ -1504,7 +1504,7 @@ class GitUtils(object):
     count = int(p2.communicate()[0])
     if p1.poll() != 0:
       raise SystemExit(_("%s does not appear to be a valid git repository")
-                       % repo)
+                       % decode(repo))
     return count
 
   @staticmethod

t/t9391-filter-repo-lib-usage.sh

@@ -160,7 +160,7 @@ test_expect_success 'other error cases' '
 		cd other &&
 
 		! python3 -c "import git_filter_repo as fr; fr.GitUtils.get_commit_count(b\".\", [\"HEAD\"])" 2>err &&
-		test_i18ngrep ". does not appear to be a valid git repository" err
+		test_i18ngrep "\. does not appear to be a valid git repository" err
 	)
 '