Fix linter error

[rafiramadhana]

Fix error when running make go-lint

➜  dagu git:(main) ✗ make go-lint
service/frontend/middleware/basic_auth_test.go:14:10: Error return value of `w.Write` is not checked (errcheck)
		w.Write([]byte("OK"))
		       ^
make: *** [Makefile:83: go-lint] Error 1

This error affects make build, so I think it is quite important to fix this

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (22f3138) 73.11% compared to head (ee08c95) 72.84%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #515      +/-   ##
==========================================
- Coverage   73.11%   72.84%   -0.27%     
==========================================
  Files          43       43              
  Lines        3678     3705      +27     
==========================================
+ Hits         2689     2699      +10     
- Misses        850      868      +18     
+ Partials      139      138       -1     

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[yohamta]

Thank you so much!