bump TiDB Operator to v1.6.0-beta.1, TiDB to v7.5.1

[csuzhangxc]

What problem does this PR solve?

What is changed and how does it work?

only bump TiDB to 7.5.1 as v8.0.0 not has not beed released yet

Code changes

• [ ] Has Go code change
• [ ] Has CI related scripts change

Tests

• [ ] Unit test
• [ ] E2E test
• [ ] Manual test
• [ ] No code

Side effects

• [ ] Breaking backward compatibility
• [ ] Other side effects:

Related changes

• [ ] Need to cherry-pick to the release branch
• [ ] Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[csuzhangxc]

/run-all-tests

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 64.16%. Comparing base (14d9ab4) to head (cfa6bee).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5591 +/- ## ========================================== + Coverage 61.49% 64.16% +2.67% ========================================== Files 235 246 +11 Lines 30335 34228 +3893 ========================================== + Hits 18653 21962 +3309 - Misses 9813 10323 +510 - Partials 1869 1943 +74 ``` | [Flag](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5591/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | Coverage Δ | | |---|---|---| | [e2e](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5591/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `33.30% <ø> (?)` | | | [unittest](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5591/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `61.48% <ø> (-0.01%)` | :arrow_down: |

[csuzhangxc]

/run-all-tests

[HuSharp]

/run-pull-e2e-kind

[HuSharp]

/run-pull-e2e-kind-tikv-scale-simultaneously

[csuzhangxc]

/run-pull-e2e-kind

[csuzhangxc]

/run-pull-e2e-kind