proxy: exclude triple logging of connect compute errors

[awarus]

Problem

Fixes #9020

Summary of changes

• Use the compute::COULD_NOT_CONNECT for connection error message;
• Eliminate logging for one connection attempt;
• Typo fix.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

5085 tests run: 4878 passed, 0 failed, 207 skipped (full report)

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Flaky tests (5)

Postgres 17

• test_multixid_wraparound_import: release-x86-64
• test_subscriber_restart: release-x86-64

Postgres 16

• test_subscriber_restart: release-x86-64

Postgres 15

• test_replica_start_scan_clog_crashed_xids: release-arm64

Postgres 14

• test_subscriber_restart: release-x86-64

Code coverage* (full report)

• functions: 31.4% (7510 of 23916 functions)
• lines: 49.6% (60289 of 121526 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
136e0a1 at 2024-10-04T13:14:32.054Z :recycle:}