refactor: remove useless git checkout after a git clone

[olblak]

While working on #1964

I released that we always run git checkout the default branch(main) after a git clone operation.
even though a git checkout is done before each source/condition/targets

This initial git checkout seems useless and generate error in some situation

We can easily reproduce the problem with the following manifests

updatecli.yaml

scms:
  default:
    kind: git 
    spec:
      url: https://github.com/crate-ci/typos.git

triggers

Console Output

+++++++++++
+ PREPARE +
+++++++++++

Loading Pipeline "test.2.yaml"

SCM repository retrieved: 1
ERROR: initial git checkout failed for repository https://github.com/crate-ci/typos.git - reference not found
ERROR: err - reference not found

As updatecli tries to run a git checkout of the default branch "main" which doesn't exist on that repository

Test

To test this pull request, you can run the following commands:

cd <to_package_directory>
go test

Additional Information

Tradeoff

Potential improvement