Update the swift-5.1-branch scheme to use swift-5.1-branch

Author: shahmishal

utils/update_checkout/update-checkout-config.json

@@ -279,21 +279,21 @@
                 "swift": "swift-5.1-branch",
                 "lldb": "swift-5.1-branch",
                 "cmark": "master",
-                "llbuild": "master",
-                "swiftpm": "master",
-                "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",
+                "llbuild": "swift-5.1-branch",
+                "swiftpm": "swift-5.1-branch",
+                "swift-syntax": "swift-5.1-branch",
+                "swift-stress-tester": "swift-5.1-branch",
+                "swift-corelibs-xctest": "swift-5.1-branch",
+                "swift-corelibs-foundation": "swift-5.1-branch",
+                "swift-corelibs-libdispatch": "swift-5.1-branch",
+                "swift-integration-tests": "swift-5.1-branch",
+                "swift-xcode-playground-support": "swift-5.1-branch",
                 "ninja": "release",
                 "icu": "release-61-1",
                 "clang-tools-extra": "swift-5.1-branch",
                 "libcxx": "swift-5.1-branch",
-                "indexstore-db": "master",
-                "sourcekit-lsp": "master"
+                "indexstore-db": "swift-5.1-branch",
+                "sourcekit-lsp": "swift-5.1-branch"
             }
         }
     }