RFR: 8262294: java/net/httpclient/ProxyAuthDisabledSchemes.java fails with HTTP/1.1 parser received no bytes

[Daniel Jeliński]

Please review this trivial fix for setting "Expect" header.

The original code added a new header every time. As a result, when the request was retried, it was sent with two Expect headers.
The new code replaces the original Expect header instead of adding a new one.

Expect header allows only one value, "100-continue", so there's no risk of overwriting some other value.

No new test. I added the bug ID to the test that was intermittently failing because of this issue. Existing tests continue to pass.

Also fixed an unintentional passthrough in `switch` case that generated duplicate logs in tests.

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Commit messages:
 - Fix duplicate expect 100

Changes: https://git.openjdk.org/jdk/pull/13224/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13224&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8262294
  Stats: 8 lines in 4 files changed: 1 ins; 4 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13224.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13224/head:pull/13224

PR: https://git.openjdk.org/jdk/pull/13224