Update grep defaults in workflow error script

This commit refines the grep functionality in the
`print_workflow_run_errors.py` script by updating default values:

- The default `--grep-pattern` is now `"[Ee]rror[: ]"`.
  Logs will be automatically filtered for this pattern if no other
  pattern is specified.
- The default `--grep-context` is now 10 lines.

If an empty string is explicitly passed to `--grep-pattern`
(e.g., `--grep-pattern ""`), grep functionality will be disabled,
and the script will fall back to printing the last N lines of the log.

Author: google-labs-jules[bot]

scripts/print_workflow_run_errors.py

@@ -159,14 +159,14 @@ def parse_repo_url_arg(url_string):
   parser.add_argument(
       "--grep-pattern", "-g",
       type=str,
-      default=None,
-      help="Extended Regular Expression (ERE) to search for in logs. If provided, log output will be filtered by grep."
+      default="[Ee]rror[: ]",
+      help="Extended Regular Expression (ERE) to search for in logs. Default: \"[Ee]rror[: ]\". If an empty string is passed, grep is disabled."
   )
   parser.add_argument(
       "--grep-context", "-C",
       type=int,
-      default=5,
-      help="Number of lines of leading and trailing context to print for grep matches. Default: 5."
+      default=10,
+      help="Number of lines of leading and trailing context to print for grep matches. Default: 10."
   )
 
   args = parser.parse_args()