fix: Increase account charecter limit (#260)

I faced an issue where a long queue name is prepended with a +, which
causes the test_account to fail. I recommend increasing the charecter.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Bug Fixes**
- Improved validation of SLURM accounts by updating the formatting of
the account check command to ensure more consistent and reliable
results.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: ChristofferCOASD

snakemake_executor_plugin_slurm/__init__.py

@@ -653,7 +653,7 @@ def test_account(self, account):
         """
         tests whether the given account is registered, raises an error, if not
         """
-        cmd = "sshare -U --format Account --noheader"
+        cmd = "sshare -U --format Account%256 --noheader"
         try:
             accounts = subprocess.check_output(
                 cmd, shell=True, text=True, stderr=subprocess.PIPE