Update ignore_template_commit to ignore checkout changes

We don't want to see diffs when running `sync` with a custom template
version, since this flag is primarily intended to be run on template
repo PRs where we don't care that the template version changes since the
actual change will only be applied once we merge the PR.

commodore/dependency_templater.py

@@ -49,12 +49,20 @@ def _ignore_cruft_json_commit_id(
                 n=0,
             )
         )[3:]
-        # If the context-less diff has exactly 2 lines and both of them start with
-        # '[-+] "commit":', we omit the diff
         if (
+            # If the context-less diff has exactly 2 lines and both of them start with
+            # '[-+] "commit":', we omit the diff
             len(minimal_diff) == 2
             and minimal_diff[0].startswith('-  "commit":')
             and minimal_diff[1].startswith('+  "commit":')
+        ) or (
+            # If the context-less diff has exactly 4 lines and the two pairs start with
+            # '[-+] "commit":' and '[-+] "checkout":', we omit the diff
+            len(minimal_diff) == 4
+            and minimal_diff[0].startswith('-  "commit":')
+            and minimal_diff[1].startswith('-  "checkout":')
+            and minimal_diff[2].startswith('+  "commit":')
+            and minimal_diff[3].startswith('+  "checkout":')
         ):
             omit = True
     # never suppress diffs in default difffunc