Disable the new GPR2 warning when compiler drivers are missing

gnatcov already takes care of emitting fatal errors in that case, so the
new warning only adds noise: disable it (like all GPR tools seem to do
anyway...).

(cherry picked from commit 7366636)

Author: pmderodat

tools/gnatcov/project.adb

@@ -1312,7 +1312,8 @@ package body Project is
          With_Runtime         => True,
          Reporter             => Create_Reporter,
          Artifacts_Info_Level => GPR2.Sources_Units,
-         Absent_Dir_Error     => GPR2.No_Error)
+         Absent_Dir_Error     => GPR2.No_Error,
+         Check_Drivers        => False)
       then
          Fatal_Error ("Could not load the project file, aborting.");
       end if;

tools/gnatcov/setup_rts.adb

@@ -237,7 +237,8 @@ package body Setup_RTS is
                                  then GPR2.Reporter.Regular
                                  else GPR2.Reporter.No_Warnings)),
          With_Runtime     => True,
-         Absent_Dir_Error => GPR2.No_Error);
+         Absent_Dir_Error => GPR2.No_Error,
+         Check_Drivers    => False);
    end Load_Project;
 
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