fix(backend): clips/updateのdescriptionで空文字を許容するように

[kakkokari-gtyih]

What

Why

Fix #15419

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]

このPRによるapi.jsonの差分

差分はこちら

--- base
+++ head
@@ -30458,7 +30458,6 @@
                       "string",
                       "null"
                     ],
-                    "minLength": 1,
                     "maxLength": 2048
                   }
                 },
@@ -31916,7 +31915,6 @@
                       "string",
                       "null"
                     ],
-                    "minLength": 1,
                     "maxLength": 2048
                   }
                 },

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[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 37.64%. Comparing base (231c2c2) to head (2d36226).

Files with missing lines	Patch %	Lines
...s/backend/src/server/api/endpoints/clips/create.ts	25.00%	3 Missing ⚠️
...s/backend/src/server/api/endpoints/clips/update.ts	25.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #15429      +/-   ##
===========================================
- Coverage    38.64%   37.64%   -1.01%     
===========================================
  Files         1607     1607              
  Lines       204774   204778       +4     
  Branches      4016     3717     -299     
===========================================
- Hits         79141    77086    -2055     
- Misses      124991   127044    +2053     
- Partials       642      648       +6     

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