Fix repositoryserver controller Immutability test

[kale-amruta]

Change Overview

The TestRepositoryServerImmutability has been failing intermittently with the error:

[2023-09-13T04:22:59.619Z]           `Operation cannot be fulfilled on repositoryservers.cr.kanister.io "test-kopia-repo-server-nb6kj": the object has been modified; please apply your changes to the latest version and try again`
[2023-09-13T04:22:59.619Z]         want:
[2023-09-13T04:22:59.619Z]           `RepositoryServer.cr.kanister.io "test-kopia-repo-server-nb6kj" is invalid: spec.repository.rootPath: Invalid value: "string": Value is immutable`

Since Repository Server Controller keeps on udpating the resource for different operations, resource version for the RepositoryServer Object keeps on changing and can result in above error. Since our goal is to test immutability for the field, this PR changes the update operation to patch operation so that we dont get above issue

Pull request type

Please check the type of change your PR introduces:

• 🚧 Work in Progress
• 🌈 Refactoring (no functional changes, no api changes)
• 🐹 Trivial/Minor
• 🐛 Bugfix
• 🌻 Feature
• 🗺️ Documentation
• 🤖 Test

Issues

• fixes #issue-number

Test Plan

• 💪 Manual
• ⚡ Unit test
• 💚 E2E

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