67dc752 cmake, test: Disable tests instead of ignoring them (Hennadii Stepanov)
bb9157d cmake, refactor: Switch to `Python3::Interpreter` imported target (Hennadii Stepanov)

Pull request description:

  This PR:

  1. Switches to a modern CMake approach by using the `Python3::Interpreter` imported target, which is more robust than using variables.

  2. Disables the `util_rpcauth_test` test explicitly instead of silently ignoring it.

  A build and test log for the case when Python is unavailable is provided below:
  ```
  $ cmake -B build
  $ cmake --build build -j 16
  $ ctest --test-dir build -j $(nproc) -R "^util"
  Internal ctest changing into directory: /bitcoin/build
  Test project /bitcoin/build
      Start 115: util_tests
      Start 117: util_trace_tests
      Start 114: util_string_tests
      Start 116: util_threadnames_tests
      Start   1: util_rpcauth_test
  1/5 Test   bitcoin#1: util_rpcauth_test ................***Not Run (Disabled)   0.00 sec
  2/5 Test #114: util_string_tests ................   Passed    0.11 sec
  3/5 Test #117: util_trace_tests .................   Passed    0.11 sec
  4/5 Test #116: util_threadnames_tests ...........   Passed    0.11 sec
  5/5 Test #115: util_tests .......................   Passed    0.13 sec

  100% tests passed, 0 tests failed out of 4

  Total Test time (real) =   0.13 sec

  The following tests did not run:
    1 - util_rpcauth_test (Disabled)
  ```

ACKs for top commit:
  purpleKarrot:
    ACK 67dc752
  janb84:
    tACK 67dc752

Tree-SHA512: 5fc7ebe31ac03f4b8a53ecfcfc1cace0f647a1d2c989651988edae96bdfbbe2dee171714e57cb028e65ead1bb40806a82d9821746451dbf005538601fd33ea88