Fix flaky querier unit test

[SungJin1212]

This PR fixes flaky querier_test.go due to race condition from https://github.com/cortexproject/cortex/blob/master/pkg/querier/querier.go#L211.

Failed logs:

WARNING: DATA RACE
Write at 0x00000396adb7 by goroutine 2291:
  github.com/cortexproject/cortex/pkg/querier.New()
      /__w/cortex/cortex/pkg/querier/querier.go:211 +0x766
  github.com/cortexproject/cortex/pkg/querier.TestQuerier_ValidateQueryTimeRange_MaxQueryLength_Series()
      /__w/cortex/cortex/pkg/querier/querier_test.go:913 +0x60d
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      /usr/local/go/src/testing/testing.go:1743 +0x44

Previous write at 0x00000396adb7 by goroutine 2[65](https://github.com/cortexproject/cortex/actions/runs/12042319929/job/33575766176?pr=6330#step:6:66)0:
  github.com/cortexproject/cortex/pkg/querier.New()
      /__w/cortex/cortex/pkg/querier/querier.go:211 +0x7[66](https://github.com/cortexproject/cortex/actions/runs/12042319929/job/33575766176?pr=6330#step:6:67)
  github.com/cortexproject/cortex/pkg/querier.TestQuerier_ValidateQueryTimeRange_MaxQueryLength.func1()
      /__w/cortex/cortex/pkg/querier/querier_test.go:873 +0x66d
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      /usr/local/go/src/testing/testing.go:1743 +0x44

Goroutine 2291 (running) created at:
  testing.(*T).Run()
      /usr/local/go/src/testing/testing.go:1743 +0x825
  testing.runTests.func1()
      /usr/local/go/src/testing/testing.go:21[68](https://github.com/cortexproject/cortex/actions/runs/12042319929/job/33575766176?pr=6330#step:6:69) +0x85
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1690 +0x226
  testing.runTests()
      /usr/local/go/src/testing/testing.go:2166 +0x8be
  testing.(*M).Run()
      /usr/local/go/src/testing/testing.go:2034 +0xf17
  main.main()
      _testmain.go:153 +0x164

Goroutine 2650 (running) created at:
  testing.(*T).Run()
      /usr/local/go/src/testing/testing.go:1743 +0x825
  github.com/cortexproject/cortex/pkg/querier.TestQuerier_ValidateQueryTimeRange_MaxQueryLength()
      /__w/cortex/cortex/pkg/querier/querier_test.go:856 +0xa0c
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1[69](https://github.com/cortexproject/cortex/actions/runs/12042319929/job/33575766176?pr=6330#step:6:70)0 +0x226
  testing.(*T).Run.gowrap1()
      /usr/local/go/src/testing/testing.go:1743 +0x44
==================
--- FAIL: TestQuerier_ValidateQueryTimeRange_MaxQueryLength_Series (0.02s)
    testing.go:1399: race detected during execution of test
--- FAIL: TestQuerier_ValidateQueryTimeRange_MaxQueryLength (0.04s)
    --- FAIL: TestQuerier_ValidateQueryTimeRange_MaxQueryLength/should_allow_query_on_short_time_range_and_rate_time_window_close_to_the_limit (0.01s)
        testing.go:1399: race detected during execution of test
--- FAIL: TestConfig_Validate (0.00s)
    testing.go:1399: race detected during execution of test
level=debug org_id=7 component=block.BaseFetcher msg="fetching meta data" concurrency=1
level=info org_id=7 component=block.BaseFetcher msg="successfully synchronized block metadata" duration=1.001395[76](https://github.com/cortexproject/cortex/actions/runs/12042319929/job/33575766176?pr=6330#step:6:77)s duration_ms=1001 cached=0 returned=0 partial=0
level=error msg="unable to run the initial blocks scan" err="context canceled"
--- FAIL: TestBlocksStoreReplicationSet_GetClientsFor_ShouldSupportRandomLoadBalancingStrategy (2.00s)
    testing.go:1399: race detected during execution of test
--- FAIL: TestBucketIndexBlocksFinder_GetBlocks (0.01s)
    testing.go:1399: race detected during execution of test
level=error msg="unable to run the initial blocks scan" err="context canceled"
FAIL
FAIL	github.com/cortexproject/cortex/pkg/querier	29.[81](https://github.com/cortexproject/cortex/actions/runs/12042319929/job/33575766176?pr=6330#step:6:82)5s

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[friedrichg]

:( I am ok with this though if it removes the problem.

Thanks!

[danielblando]

Looks like we already have other tests without the parallel for the same "New" function