fix(backend): follow-up of #17415

[kakkokari-gtyih]

What

Cacheをdisposeするように

Why

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[github-actions]

Backend memory usage comparison

Before GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	303.67 MB	307.45 MB	+3.78 MB	+1.24%
VmHWM	303.67 MB	307.45 MB	+3.78 MB	+1.24%
VmSize	23169.11 MB	23172.22 MB	+3.10 MB	+0.01%
VmData	1369.13 MB	1372.65 MB	+3.51 MB	+0.25%

After GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	303.78 MB	307.47 MB	+3.69 MB	+1.21%
VmHWM	303.78 MB	307.47 MB	+3.69 MB	+1.21%
VmSize	23169.28 MB	23172.63 MB	+3.35 MB	+0.01%
VmData	1369.30 MB	1373.07 MB	+3.76 MB	+0.27%

After Request

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	304.20 MB	307.84 MB	+3.63 MB	+1.19%
VmHWM	304.20 MB	307.84 MB	+3.63 MB	+1.19%
VmSize	23169.28 MB	23172.72 MB	+3.43 MB	+0.01%
VmData	1369.38 MB	1373.15 MB	+3.77 MB	+0.27%

See workflow logs for details

[github-actions]

このPRによるapi.jsonの差分
差分はありません。
Get diff files from Workflow Page

[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 24.89%. Comparing base (6237001) to head (3e65190).

Files with missing lines	Patch %	Lines
.../backend/src/server/oauth/OAuth2ProviderService.ts	0.00%	10 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #17505      +/-   ##
===========================================
- Coverage    24.93%   24.89%   -0.04%     
===========================================
  Files         1160     1160              
  Lines        39550    39555       +5     
  Branches     11016    11008       -8     
===========================================
- Hits          9861     9848      -13     
- Misses       23791    23806      +15     
- Partials      5898     5901       +3     

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