Fix backup numbering when .tar.gz files are decompressed to .tar (#404)

* Fix backup numbering when .tar.gz files are decompressed to .tar

* pre-commit auto-fixes

* simplify backup() numbering logic

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: NicoPhase

src/custodian/utils.py

@@ -20,7 +20,17 @@ def backup(filenames, prefix="error", directory="./") -> None:
             series of error.1.tar.gz, error.2.tar.gz, ... will be generated.
         directory (str): directory where the files exist
     """
-    num = max([0] + [int(file.split(".")[-3]) for file in glob(os.path.join(directory, f"{prefix}.*.tar.gz"))])
+    backup_files = glob(os.path.join(directory, f"{prefix}.*.tar*"))
+    nums = [0]
+    for file in backup_files:
+        try:
+            if file.endswith(".tar.gz"):
+                nums.append(int(file.split(".")[-3]))
+            elif file.endswith(".tar"):
+                nums.append(int(file.split(".")[-2]))
+        except (ValueError, IndexError):
+            continue
+    num = max(nums)
     prefix = f"{prefix}.{num + 1}"
     filename = os.path.join(directory, f"{prefix}.tar.gz")
     logging.info(f"Backing up run to {filename}")