fix: write the config file with owner-only permissions

[nikosavola]

• the file holds the api token but was created 0644 via viper's default

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.86%. Comparing base (176547e) to head (fd8e117).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/cmdutil/config.go	33.33%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #306      +/-   ##
==========================================
+ Coverage   32.46%   32.86%   +0.39%     
==========================================
  Files         141      141              
  Lines        9016     9020       +4     
==========================================
+ Hits         2927     2964      +37     
+ Misses       5974     5932      -42     
- Partials      115      124       +9     

Flag	Coverage Δ
unittests	32.86% <33.33%> (+0.39%)	⬆️

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