pmb.helpers.repo.update: support PMB_APK_FORCE_MISSING_REPOSITORIES (MR 2505)

Do not abort if one or more APKINDEX files cannot be downloaded, if
PMB_APK_FORCE_MISSING_REPOSITORIES is set. This is needed when
bootstrapping new stable branches. The same environment variable is
already used in pmbootstrap code to pass --force-missing-repositories to
apk in pmb.chroot.apk.install_run_apk().

pmb/helpers/repo.py

@@ -215,18 +215,28 @@ def update(arch: Arch | None = None, force: bool = False, existing_only: bool =
     )
 
     # Download and move to right location
+    missing_ignored = False
     for i, (url, target) in enumerate(outdated.items()):
         pmb.helpers.cli.progress_print(i / len(outdated))
         temp = pmb.helpers.http.download(url, "APKINDEX", False, logging.DEBUG, True, True)
         if not temp:
-            logging.info("NOTE: check the [mirrors] section in 'pmbootstrap config'")
-            raise NonBugError("getting APKINDEX from binary package mirror failed!")
+            if os.environ.get("PMB_APK_FORCE_MISSING_REPOSITORIES") == "1":
+                missing_ignored = True
+                continue
+            else:
+                logging.info("NOTE: check the [mirrors] section in 'pmbootstrap config'")
+                raise NonBugError("getting APKINDEX from binary package mirror failed!")
         target_folder = os.path.dirname(target)
         if not os.path.exists(target_folder):
             pmb.helpers.run.root(["mkdir", "-p", target_folder])
         pmb.helpers.run.root(["cp", temp, target])
     pmb.helpers.cli.progress_flush()
 
+    if missing_ignored:
+        logging.warn_once(
+            "NOTE: ignoring missing APKINDEX due to PMB_APK_FORCE_MISSING_REPOSITORIES=1 (fine during bootstrap)"
+        )
+
     return True