maybe-uninitialized variable in TestFKDTree

[iarspider]

In CPP20 IBs, the following warnings are emitted:

.../src/CommonTools/RecoAlgos/test/FKDTree_t.cpp: In member function 'test2D':
  .../src/CommonTools/RecoAlgos/test/FKDTree_t.cpp:48:13: warning: 'y' may be used uninitialized [-Wmaybe-uninitialized]
    48 |       float y;
      |             ^
.../src/CommonTools/RecoAlgos/test/FKDTree_t.cpp: In member function 'test3D':
  .../cms/cmssw/CMSSW_13_3_CPP20_X_2023-07-24-1100/src/CommonTools/RecoAlgos/test/FKDTree_t.cpp:98:13: warning: 'y' may be used uninitialized [-Wmaybe-uninitialized]
    98 |       float y;
      |             ^

(this was spotted initially in #31379 (review), but not followed up)

[cmsbuild]

A new Issue was created by @iarspider .

@Dr15Jones, @perrotta, @dpiparo, @rappoccio, @makortel, @smuzaffar can you please review it and eventually sign/assign? Thanks.

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[iarspider]

assign reconstruction

[cmsbuild]

New categories assigned: reconstruction

@mandrenguyen,@clacaputo you have been requested to review this Pull request/Issue and eventually sign? Thanks

[iarspider]

Closed via #42626