gh-125522: Remove bare except in test_zlib.test_flushes

[simple-is-great]

This is a simple rewrite of the test to avoid bare except and make the test's intention clearer.

• zlib only has single exception(zlib.error) but explicitly displaying error name would be better..!
• Reference: https://docs.python.org/3/library/zlib.html

• Issue: avoid bare except: in stdlib #125522

[cpython-cla-bot]

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[simple-is-great]

cc: @corona10

[corona10]

@simple-is-great See the example of

cpython/Lib/test/test__opcode.py

Lines 15 to 17 in 914356f

	with self.subTest(opcode=op, func=func):
	self.assertIsInstance(func(op), bool)
	self.assertEqual(func(op), expected)

[skirpichev]

One formatting nitpick, otherwise LGTM.

[corona10]

lgtm

[miss-islington-app]

Thanks @simple-is-great for the PR, and @corona10 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-126327 is a backport of this pull request to the 3.13 branch.

[bedevere-app]

GH-126328 is a backport of this pull request to the 3.12 branch.