pre-commit: include vmtest/rootfsbuild.py in vermin

The only error is about typing.Literal, which we already have guarded in
a sys.version_info check, so we can add novermin.

Signed-off-by: Omar Sandoval <osandov@osandov.com>

.pre-commit-config.yaml

@@ -37,8 +37,6 @@ repos:
         # The vmtest package in general should adhere to the same version
         # requirements as drgn, with the following exceptions: The manage &
         # kbuild scripts are used by Github Actions and need not be broadly
-        # compatible. The rootfsbuild script is used to create test environments
-        # for other architectures, and is sufficiently advanced that it isn't
-        # expected to be run by most users or even most developers.
-        exclude: "^vmtest/(manage|kbuild|rootfsbuild).py$"
+        # compatible.
+        exclude: "^vmtest/(manage|kbuild).py$"
         args: ['-t=3.6-', '--violations', '--eval-annotations']

vmtest/rootfsbuild.py

@@ -12,7 +12,7 @@ if typing.TYPE_CHECKING:
     if sys.version_info < (3, 8):
         from typing_extensions import Literal
     else:
-        from typing import Literal
+        from typing import Literal  # novermin
 
 from vmtest.config import ARCHITECTURES, HOST_ARCHITECTURE, Architecture