pmb.chroot.apk: Use unpacking operator to create command in install_run_apk() (MR 2525)

The unpacking operator can unpack any iterable of any type, unlike the +
operator which only works on some sequences and requires them to be of
the same type usually. Using it allows us to get rid of the line that
disables the "operator" error code for this function.

pmb/chroot/apk.py

@@ -125,8 +125,6 @@ def packages_get_locally_built_apks(package_list: list[str], arch: Arch) -> list
     return local
 
 
-# FIXME: list[Sequence[PathString]] weirdness
-# mypy: disable-error-code="operator"
 def install_run_apk(
     to_add: list[str], to_add_local: list[Path], to_del: list[str], chroot: Chroot
 ) -> None:
@@ -173,12 +171,12 @@ def install_run_apk(
         pmb.chroot.init(chroot)
 
     # FIXME: use /mnt/pmb… until MR 2351 is reverted (pmb#2388)
-    user_repo = []
+    user_repo: list[PathString] = []
     for channel in pmb.config.pmaports.all_channels():
         user_repo += ["--repository", context.config.work / "packages" / channel]
 
     for i, command in enumerate(commands):
-        command = user_repo + command
+        command = [*user_repo, *command]
 
         # Ignore missing repos before initial build (bpo#137)
         if os.getenv("PMB_APK_FORCE_MISSING_REPOSITORIES") == "1":