RFR: 8358048: java/net/httpclient/HttpsTunnelAuthTest.java incorrectly calls Thread::stop

[Jaikiran Pai]

Can I please get a review of this test-only change which fixes an accidental use of `Thread.stop()`? This addresses https://bugs.openjdk.org/browse/JDK-8358048.

The test during it's termination attempts to close the `ProxyServer` and invokes `ProxyServer.stop()`. The `ProxyServer` does not have a `stop()` method of its own but since the `ProxyServer` is a `java.lang.Thread`, calling `stop()` on the `ProxyServer` ends up calling the `Thread.stop()`. The use of `stop()` in this test is accidental and the test should have used `ProxyServer.close()`.

The commit in this PR fixes the issue by removing the use of `ProxyServer.stop()`. The test continues to pass with this change.

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Commit messages:
 - 8358048: java/net/httpclient/HttpsTunnelAuthTest.java incorrectly calls Thread::stop

Changes: https://git.openjdk.org/jdk/pull/26473/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26473&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358048
  Stats: 6 lines in 1 file changed: 1 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/26473.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26473/head:pull/26473

PR: https://git.openjdk.org/jdk/pull/26473