fix: Use base64 to encode not utf-8 bytes

[XuanYang-cn]

See also: #45654

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[ci-v2-notice]
Notice: We are gradually rolling out the new ci-v2 system.

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@XuanYang-cn go-sdk check failed, comment rerun go-sdk can trigger the job again.

[codecov]

Codecov Report

❌ Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.48%. Comparing base (aa0870d) to head (4cd2cc6).
⚠️ Report is 17 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/storage/rw.go	0.00%	2 Missing ⚠️
internal/flushcommon/syncmgr/pack_writer_v2.go	0.00%	1 Missing ⚠️
internal/querynodev2/segments/collection.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #45655       +/-   ##
===========================================
- Coverage   83.19%   76.48%    -6.71%     
===========================================
  Files         521     1875     +1354     
  Lines       81430   292657   +211227     
===========================================
+ Hits        67744   223846   +156102     
- Misses      13686    61376    +47690     
- Partials        0     7435     +7435     

Components	Coverage Δ
Client	78.17% <ø> (∅)
Core	83.19% <93.75%> (+<0.01%)	⬆️
Go	74.59% <69.40%> (∅)

Files with missing lines	Coverage Δ
internal/util/hookutil/cipher.go	85.93% <100.00%> (ø)
internal/flushcommon/syncmgr/pack_writer_v2.go	74.82% <0.00%> (ø)
internal/querynodev2/segments/collection.go	86.26% <0.00%> (ø)
internal/storage/rw.go	76.23% <0.00%> (ø)

... and 1353 files with indirect coverage changes

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@XuanYang-cn cpu-e2e job failed, comment /run-cpu-e2e can trigger the job again.

[XuanYang-cn]

/ci-rerun-ut-integration

[mergify]

@XuanYang-cn cpu-e2e job failed, comment /run-cpu-e2e can trigger the job again.

[XuanYang-cn]

/run-cpu-e2e

[XuanYang-cn]

/ci-rerun-ut-integration

[sre-ci-robot]

[ci-v2-notice]
Notice: We are gradually rolling out the new ci-v2 system.

• Legacy CI jobs remain unaffected, you can just ignore ci-v2 if you don't want to run it.
• Additional "ci-v2/*" checkers will run for this PR to ensure the new ci-v2 system is working as expected.
• For tests that exist in both v1 and v2, passing in either system is considered PASS.

To rerun ci-v2 checks, comment with:

• /ci-rerun-code-check // for ci-v2/code-check
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• /ci-rerun-ut-go // for ci-v2/ut-go
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