Force UITests locale en_US

... otherwise they fail e.g. on Russian locale like this:

$ /opt/lo/bin/make UITest_calc_tests7 UITEST_TEST_NAME="tdf123479.tdf123479.test_tdf123479_Crash_ScFormulaResult_GetMatrixFormulaCellToken"
C:/cygwin64/opt/lo/bin/make -j 12 -rs -f C:/lo/src/core2/Makefile.gbuild UITest_calc_tests7
...
[UIT] calc_tests7
...
Execution time for tdf123479.tdf123479.test_tdf123479_Crash_ScFormulaResult_GetMatrixFormulaCellToken: 3.847
tearDown: calling terminate()...
...done
FAIL

======================================================================
FAIL: test_tdf123479_Crash_ScFormulaResult_GetMatrixFormulaCellToken (tdf123479.tdf123479)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:/lo/src/core2/sc/qa/uitest/calc_tests7/tdf123479.py", line 42, in test_tdf123479_Crash_ScFormulaResult_GetMatrixFormulaCellToken
    self.assertEqual(get_state_as_dict(edArg2)["Text"], "OFFSET($Data.$A$2:$Data.$A$4,0,COLUMN()-3)")
AssertionError: 'OFFSET($Data.$A$2:$Data.$A$4;0;COLUMN()-3)' != 'OFFSET($Data.$A$2:$Data.$A$4,0,COLUMN()-3)'
- OFFSET($Data.$A$2:$Data.$A$4;0;COLUMN()-3)
?                             ^ ^
+ OFFSET($Data.$A$2:$Data.$A$4,0,COLUMN()-3)
?                             ^ ^


----------------------------------------------------------------------
Ran 1 test in 77.822s

FAILED (failures=1)
Tests run: 1
Tests failed: 1
Tests errors: 0
Tests skipped: 0

Change-Id: I65a199cc3f9667b8a2d72ba09ceb68732da3ec88
Reviewed-on: https://gerrit.libreoffice.org/70127Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

solenv/gbuild/UITest.mk

@@ -46,6 +46,8 @@ $(call gb_UITest_get_clean_target,%) :
 
 ifneq ($(DISABLE_PYTHON),TRUE)
 
+# qadevOOo/qa/registrymodifications.xcu is copied to user profile directory to ensure en_US locale;
+# this might be overwritten later when gb_UITest_use_config is set
 .PHONY : $(call gb_UITest_get_target,%)
 $(call gb_UITest_get_target,%) :| $(gb_UITest_DEPS)
 ifneq ($(gb_SUPPRESS_TESTS),)
@@ -54,7 +56,8 @@ else
 	$(call gb_Output_announce,$*,$(true),UIT,2)
 	$(call gb_Helper_abbreviate_dirs,\
 		rm -rf $(dir $(call gb_UITest_get_target,$*)) && \
-		mkdir -p $(dir $(call gb_UITest_get_target,$*)) && \
+		mkdir -p $(dir $(call gb_UITest_get_target,$*))/user/user && \
+		cp $(SRCDIR)/qadevOOo/qa/registrymodifications.xcu $(dir $(call gb_UITest_get_target,$*))/user/user/ && \
 		$(if $(gb_UITest__interactive),, \
 		    rm -fr $@.core && mkdir -p $(dir $(call gb_UITest_get_target,$*))user/ && mkdir $@.core && cd $@.core && ) \
 		$(if $(gb_UITest_use_config), \