use raw strings to avoid escaping (#50322)

diff --git a/packages/flutter_tools/lib/src/project.dart b/packages/flutter_tools/lib/src/project.dart
index 2d01fcc..d227d8e 100644
--- a/packages/flutter_tools/lib/src/project.dart
+++ b/packages/flutter_tools/lib/src/project.dart
@@ -409,7 +409,7 @@
       } on FileNotFoundException {
         // iOS tooling not found; likely not running OSX; let [fromPlist] be null
       }
-      if (fromPlist != null && !fromPlist.contains('\$')) {
+      if (fromPlist != null && !fromPlist.contains(r'$')) {
         // Info.plist has no build variables in product bundle ID.
         return fromPlist;
       }