Fix static analysis warning C4146 in caltest.cpp

[Hanumant Shinde (therealhshinde)]

Fix

Replace two -2147483648 test inputs in caltest.cpp with INT32_MIN. MSVC parses the decimal magnitude as unsigned before applying unary minus, producing C4146; INT32_MIN expresses the intended signed boundary directly without changing test behavior.

The change also records the fix as permanent Microsoft patch 030-MSFT-Patch-Fix_MSVC_C4146_caltest.patch so it survives future upstream ICU source imports.

Internal tracking: AB#164343

Compiler verification

Before

caltest.cpp(5928,37): warning C4146: unary minus operator applied to unsigned type, result still unsigned
caltest.cpp(6070,30): warning C4146: unary minus operator applied to unsigned type, result still unsigned
996 Warning(s), 0 Error(s)

After

No C4146 findings
994 Warning(s), 0 Error(s)

• Exactly the two target warning signatures were removed.
• No new warning signatures were introduced.

Test verification

• Built intltest Release x64 with Visual Studio 2022/MSVC.
• Ran the complete format/CalendarTest suite: all tests passed.
• Verified patch 030 applies cleanly to the pre-fix commit and produces the exact source blob from the fix commit.

[Hanumant Shinde (therealhshinde)]

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