TST: fix shebang typo
Fix shebang typo in generate_legacy_storage_files.py

- [x] closes #21306
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21307?src=pr&el=h1) Report
> Merging [#21307](https://codecov.io/gh/pandas-dev/pandas/pull/21307?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4274b840e64374a39a0285c2174968588753ec35?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21307/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21307?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21307   +/-   ##
=======================================
  Coverage   91.85%   91.85%           
=======================================
  Files         153      153           
  Lines       49546    49546           
=======================================
  Hits        45509    45509           
  Misses       4037     4037
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.25% <ø> (ø)` | :arrow_up: |
| #single | `41.87% <ø> (ø)` | :arrow_up: |


------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21307?src=pr&el=footer). Last update [4274b84...5550cfb](https://codecov.io/gh/pandas-dev/pandas/pull/21307?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
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