All instances of master in tests should be checked and updated to main

[JonruAlveus]

Given the default branch name is now main, a number of integration tests fail to run because they are looking for the master branch. We should check all instances of master and update to main if appropriate.

[JonruAlveus]

@nickfloyd @timrogers I've made a start on this (see attached PR). As I'm going through the integration tests I'm noticing a few issues, as I can't actually run half of the tests. Are you happy if I extend this and:

• Change attributes for organisation tests from IntegrationTest to OrganizationTest
• Change constructors to only provide the client and repository and having usings in each test to create the test specific resources
  • Changing this because I don't have an organisation to test against and I can't run the tests if the constructor creates the organisation data for tests which don't use organisations
• (Re)merging free and organisation tests where appropriate so they can be kept under the same class if they do the same thing
• Fixing namespaces
  • What's the policy here? Namespaces follow folder structure or everything has a common namespace? At the moment there's a mixture of common namespace, folder namespace and no namespace.

Cheers!

[JonruAlveus]

See #2492 for possibly a better way of doing these tests with base classes.