FindLAPACK: Distinguish check result variable name from FindBLAS

Since commit 192a9182f8 (FindLAPACK: MKL clean up and fix for windows,
2013-10-08, v3.0.0-rc1~538^2), FindLAPACK accidentally used FindBLAS's
`BLAS_` prefix for some of its check results.

Since commit 5b8f69ebe9 (FindBLAS: Detect implicitly linked BLAS
library, 2018-08-28, v3.13.0-rc1~150^2~2), FindBLAS stores a check
result in a plain `BLAS_WORKS` variable.  The typo in FindLAPACK happens
to cause a collision with that name.

The typo was already fixed in post-3.13 development as part of other
work in commit 8b63265ea5 (FindLAPACK: Unify internal variables related
to MKL, 2018-11-18).  Fix the typo in the 3.13 version of FindLAPACK to
avoid the collision.  Otherwise it could cause FindLAPACK to incorrectly
determine that a certain library combination does not work (or
incrrectly that it works).

Fixes: #18860

Modules/FindLAPACK.cmake

@@ -316,7 +316,7 @@ if (BLA_VENDOR MATCHES "Intel" OR BLA_VENDOR STREQUAL "All")
     if (NOT ${_LIBRARIES})
       check_lapack_libraries(
         ${_LIBRARIES}
-        BLAS
+        LAPACK
         ${LAPACK_mkl_SEARCH_SYMBOL}
         ""
         ""
@@ -329,7 +329,7 @@ if (BLA_VENDOR MATCHES "Intel" OR BLA_VENDOR STREQUAL "All")
       if (NOT ${_LIBRARIES})
         check_lapack_libraries(
           ${_LIBRARIES}
-          BLAS
+          LAPACK
           ${LAPACK_mkl_SEARCH_SYMBOL}
           ""
           "${IT}"