[lit][NFC] Avoid unintended -EMPTY suffix in check prefix (#99690)

FileCheck has special handline for the `-EMPTY` suffix, that should
match empty lines. Overloading the suffix can be a source of confusion
when reading tests. Additionally, the current implementation seems to
match the following expressions, which appears to be a bug in FileCheck.

Author: ilovepi

llvm/utils/lit/tests/Inputs/shtest-env/env-calls-env.txt

@@ -1,10 +1,10 @@
 # Check that internal env can call internal env.
 
 # RUN: env env %{python} print_environment.py \
-# RUN: | FileCheck -check-prefix=CHECK-2-EMPTY %s
+# RUN: | FileCheck -check-prefix=CHECK-2-EMPTY-ARGS %s
 #
-# CHECK-2-EMPTY: BAR = 2
-# CHECK-2-EMPTY: FOO = 1
+# CHECK-2-EMPTY-ARGS: BAR = 2
+# CHECK-2-EMPTY-ARGS: FOO = 1
 
 # RUN: env FOO=2 env BAR=1 %{python} print_environment.py \
 # RUN: | FileCheck -check-prefix=CHECK-2-VAL %s