Add a space before "However" in update-build-files's "... BUILD fil…

…es found.However, ..." (#20861)

Currently, running `pants update-build-files ::` prints a message that's
slightly misformatted, where there's no space after the first sentence.
This adds a space:

Before:

```
15:27:34.28 [INFO] No required changes to BUILD files found.However, there may still be deprecations that `update-build-files` doesn't know how to fix. See https://www.pantsbuild.org/2.22/docs/releases/upgrade-tips for upgrade tips.
```

After:

```
15:29:00.90 [INFO] No required changes to BUILD files found. However, there may still be deprecations that `update-build-files` doesn't know how to fix. See https://www.pantsbuild.org/2.22/docs/releases/upgrade-tips for upgrade tips.
```

src/python/pants/core/goals/update_build_files.py

@@ -277,14 +277,18 @@ async def update_build_files(
         if change_descriptions
     )
     if not changed_build_files:
-        msg = "No required changes to BUILD files found."
+        parts = ["No required changes to BUILD files found."]
         if not update_build_files_subsystem.check:
-            msg += softwrap(
-                f"""
-                However, there may still be deprecations that `update-build-files` doesn't know
-                how to fix. See {doc_url('docs/releases/upgrade-tips')} for upgrade tips.
-                """
+            parts.append(
+                softwrap(
+                    f"""
+                    However, there may still be deprecations that `update-build-files` doesn't know
+                    how to fix. See {doc_url('docs/releases/upgrade-tips')} for upgrade tips.
+                    """
+                )
             )
+
+        msg = " ".join(parts)
         logger.info(msg)
         return UpdateBuildFilesGoal(exit_code=0)