log the spe_variables only if present

src/mpsd_software_manager/mpsd_software.py

@@ -606,10 +606,11 @@ def record_script_execution_summary(
                 f.write(f"{datetime.datetime.now().isoformat()}, {cmd_line}\n")
                 # logs script version
                 f.write(f"MPSD Software manager version: {__version__}\n")
-                f.write(
-                    f"Spack environments branch: {spe_branch} "
-                    f"(commit hash: {spe_commit_hash})\n"
-                )
+                if spe_branch and spe_commit_hash:
+                    f.write(
+                        f"Spack environments branch: {spe_branch} "
+                        f"(commit hash: {spe_commit_hash})\n"
+                    )
 
 
 def clone_repo(