Updated master/main branches error info

repo2docker/contentproviders/git.py

@@ -45,10 +45,10 @@ class Git(ContentProvider):
                 self.log.error(
                     f"Failed to check out ref {ref}", extra=dict(phase=R2dState.FAILED)
                 )
-                if ref == "main":
+                if ref == "master" or ref == "main":
                     msg = (
-                        "Failed to check out the 'main' branch. "
-                        "Maybe the default branch is not named 'main' "
+                        f"Failed to check out the '{ref}' branch. "
+                        f"Maybe the default branch is not named '{ref}' "
                         "for this repository.\n\nTry not explicitly "
                         "specifying `--ref`."
                     )

tests/external/reproductions.repos.yaml

@@ -12,12 +12,12 @@
 # Test that a full remote/ref works
 - name: Binder Examples - Requirements
   url: https://github.com/binder-examples/requirements
-  ref: origin/master
+  ref: origin/main
   verify: python -c 'import matplotlib'
 # Test that ref is added to branch if not present
 - name: Binder Examples - Requirements
   url: https://github.com/binder-examples/requirements
-  ref: master
+  ref: main
   verify: python -c 'import matplotlib'
 # Test that tags work + ref is added to tag if not present
 - name: Binder Examples - Requirements