fix: use mkdirall when creating ~/.ssh dir to allow for the case where it already exists

[krancour]

This fixes a problem that only occurs when using ssh to interact with a remote repo.

We re-setup auth mechanisms every time we load an already-cloned repo from disk because the possibility always exists that for a long-running promotion step, credentials for the repo have been updated between two executions of that step. I am confident this is the right thing to do, however, when using SSH, there is an os.Mkdir() call that can fail because the directory it attempts to create would have been created by the previous execution of the auth setup logic.

This PR solves that problem by using os.MkdirAll() instead, as that will not error if the directory already exists.

Part of #2492

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 49.11%. Comparing base (686b0d4) to head (99477fc).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/controller/git/base_repo.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2708   +/-   ##
=======================================
  Coverage   49.11%   49.11%           
=======================================
  Files         270      270           
  Lines       19328    19328           
=======================================
  Hits         9492     9492           
  Misses       9217     9217           
  Partials      619      619           

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