Prevents printing attempt for binary logs

Previously a binary log file would cause `show_logs` to crash the whole
snakemake workflow execution with a `UnicodeDecodeError`.

Closes #2826

snakemake/logging.py

@@ -506,6 +506,9 @@ def show_logs(logs):
                 except FileNotFoundError:
                     yield f"Logfile {f} not found."
                     return
+                except UnicodeDecodeError:
+                    yield f"Logfile {f} is not a text file."
+                    return
                 lines = content.splitlines()
                 logfile_header = f"Logfile {f}:"
                 if not lines: