Increase HTTP connectTimeout test threshold to match gRPC

[thswlsqls]

Description

• AbstractHttpTelemetryExporterTest.connectTimeout() asserts the failed export returns in <1s. That is flaky: connection failures to a non-routable IP take 1-5s depending on OS/network.
• The sibling gRPC base AbstractGrpcTelemetryExporterTest was already relaxed <1s→<6s in PR Fix OkHttpGrpcSender to properly await executor shutdown #7840, but the HTTP base was missed — an incomplete fix.
• This mirrors that change with the same comment. Intent is unchanged — the export must still fail well before the default 10s connect timeout.
• Related: PR Fix OkHttpGrpcSender to properly await executor shutdown #7840 (commit 92d23b2), issue OkHttpGrpcSender.shutdown() does not properly await executor thread termination #7827.

Testing done

• No new test — this is a test-only change to the shared abstract base; the assertion itself is the test.
• ./gradlew :exporters:otlp:testing-internal:check passed (module has no own tests).
• ./gradlew :exporters:otlp:all:testOkHttpVersionLATEST :exporters:otlp:all:testJdkHttpSender passed; all six connectTimeout() cases (span/metric/log × OkHttp/JdkSender) green.
• No public API change (internal test package); no CHANGELOG, no apidiff.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.77%. Comparing base (824334c) to head (06a8268).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8494   +/-   ##
=========================================
  Coverage     78.77%   78.77%           
  Complexity     8579     8579           
=========================================
  Files          1009     1009           
  Lines         28993    28993           
  Branches       3599     3599           
=========================================
  Hits          22839    22839           
  Misses         5311     5311           
  Partials        843      843           

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