fixup! Tor Browser localization migration scripts.

Bug 42221: Migrate downloads warning strings to Fluent.

tools/torbrowser/l10n/migrations/bug-42210-download-warning.py

+import fluent.syntax.ast as FTL
+from fluent.migrate.helpers import transforms_from
+from fluent.migrate.transforms import CONCAT, COPY, REPLACE
+
+
+def migrate(ctx):
+    legacy_path = "torbutton.properties"
+
+    ctx.add_transforms(
+        "tor-browser.ftl",
+        "tor-browser.ftl",
+        transforms_from(
+            """
+downloads-tor-warning-title = { COPY(path, "torbutton.download.warning.title") }
+downloads-tor-warning-dismiss-button = { COPY(path, "torbutton.download.warning.dismiss") }
+""",
+            path=legacy_path,
+        )
+        + [
+            # Replace "%S" with link to Tails website.
+            FTL.Message(
+                id=FTL.Identifier("downloads-tor-warning-description"),
+                value=REPLACE(
+                    legacy_path,
+                    "torbutton.download.warning.description",
+                    {
+                        "%1$S": CONCAT(
+                            FTL.TextElement('<a data-l10n-name="tails-link">'),
+                            COPY(
+                                legacy_path,
+                                "torbutton.download.warning.tails_brand_name",
+                            ),
+                            FTL.TextElement("</a>"),
+                        )
+                    },
+                ),
+            ),
+        ],
+    )