resource group: use inner keyspace id rather outside

[lhy1024]

What problem does this PR solve?

Issue Number: ref #9296

What is changed and how does it work?

use inner keyspace id rather outside to avoid tidb forget pass keyspace id when putResourceGroup

Check List

Tests

• Unit test
• Manual test

File: tidb.toml
keyspace-name = "SYSTEM"

File: tikv.toml
[storage]
enable-ttl = true
api-version = 2

cd ~/tidb
NEXT_GEN=1 make server
cd ~/pd
NEXT_GEN=1 make pd-server
tiup playground nightly --kv 3 --tiflash 0 --host 0.0.0.0 --db.binpath=~/tidb/bin/tidb-server --pd.binpath=~/pd/bin/pd-server --db.config=~/tidb.toml --kv.config=~/tikv.toml

cd tests/integrationtest;                                                                                                                       ~/tidb
./mysql_tester -port 4000 --check-error=true --collation-disable=false --record ddl/resource_group
./t/ddl/resource_group.test: ok! 16 test cases passed, take time 1.441095362 s

Great, All tests passed

Release note

None.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: okJiang, rleungx

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• OWNERS [rleungx]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-07-03 06:32:24.852821739 +0000 UTC m=+1549397.576000721: ☑️ agreed by rleungx.
• 2025-07-03 08:36:04.977707253 +0000 UTC m=+1556817.700886232: ☑️ agreed by okJiang.

[codecov]

Codecov Report

Attention: Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.18%. Comparing base (b88e47d) to head (1d3791b).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9475      +/-   ##
==========================================
- Coverage   76.20%   76.18%   -0.02%     
==========================================
  Files         481      481              
  Lines       75538    75551      +13     
==========================================
- Hits        57560    57559       -1     
- Misses      14405    14421      +16     
+ Partials     3573     3571       -2     

Flag	Coverage Δ
unittests	76.18% <95.45%> (-0.02%)	⬇️

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