[Update Checkout] Update scheme for release/5.3

Author: shahmishal

utils/update_checkout/update-checkout-config.json

@@ -282,19 +282,19 @@
        "release/5.3": {
             "aliases": ["release/5.3", "swift/release/5.3"],
             "repos": {
-                "llvm-project": "swift/master",
-                "swift": "master",
-                "cmark": "master",
+                "llvm-project": "swift/release/5.3",
+                "swift": "release/5.3",
+                "cmark": "release/5.3",
                 "llbuild": "release/5.3",
                 "swift-tools-support-core": "release/5.3",
                 "swiftpm": "release/5.3",
-                "swift-syntax": "master",
-                "swift-stress-tester": "master",
-                "swift-corelibs-xctest": "master",
-                "swift-corelibs-foundation": "master",
-                "swift-corelibs-libdispatch": "master",
-                "swift-integration-tests": "master",
-                "swift-xcode-playground-support": "master",
+                "swift-syntax": "release/5.3",
+                "swift-stress-tester": "release/5.3",
+                "swift-corelibs-xctest": "release/5.3",
+                "swift-corelibs-foundation": "release/5.3",
+                "swift-corelibs-libdispatch": "release/5.3",
+                "swift-integration-tests": "release/5.3",
+                "swift-xcode-playground-support": "release/5.3",
                 "ninja": "release",
                 "icu": "release-65-1",
                 "cmake": "v3.16.5",