[jdk17u-dev] RFR: 8346049: jdk/test/lib/security/timestamp/TsaServer.java warnings

[Goetz Lindenmaier]

I backport this for parity with 17.0.16-oracle.

verified with 
test/jdk/sun/security/tools/jarsigner/TsacertOptionTest.java
test/jdk/sun/security/tools/jarsigner/TimestampCheck.java
which use this class.

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Commit messages:
 - Backport 1eb54e4228ba9319ac2f980055ed366dd861ec0b

Changes: https://git.openjdk.org/jdk17u-dev/pull/3447/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=3447&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346049
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/3447.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/3447/head:pull/3447

PR: https://git.openjdk.org/jdk17u-dev/pull/3447