fix(relax): fix Test_RELAX failure after removing PARAM global dependency

Symptom:
MODULE_RELAX_relax_new_relax failed. relax_step did nothing and all
taud/latvec values stayed at their initial values.

Root cause:
Commit 977855a replaced the global PARAM.input in Test_RELAX with a
local Input_para inp member, but missed three parameters that had been
silently inherited from the global state.

The inheritance worked because GoogleTest runs test suites in definition
order: Test_SETGRAD runs first and leaves the following values in the
global PARAM.input, which Test_RELAX reused without setting them:
  - calculation = cell-relax
  - force_thr    = 0.001
  - fixed_axes   = a

After the commit each test class has its own local inp, so this hidden
sharing was lost:
  - calculation defaults to scf, so setup_gradient returns true
    immediately and relax_step does nothing.
  - force_thr defaults to -1, which changes line_search convergence
    behavior.
  - fixed_axes defaults to None, which skips the stress constraint
    branch and changes cell movement.

Fix:
Explicitly set the three previously-inherited parameters in
Test_RELAX::SetUp():
  inp.calculation = cell-relax;
  inp.force_thr   = 0.001;
  inp.fixed_axes  = a;

Lessons learned:
When removing a global-variable dependency, audit every field read by
the code under test, including fields implicitly left behind by other
test suites. Each test should be self-contained and not rely on
inter-test-suite execution order.

Author: abacus_fixer

source/source_relax/test/relax_test.cpp

@@ -182,6 +182,9 @@ class Test_RELAX : public testing::Test
             int nstep = 3;
             int nat = 5;
             double energy;
+            inp.calculation = "cell-relax";
+            inp.force_thr = 0.001;
+            inp.fixed_axes = "a";
             inp.stress_thr = 0.01;
             inp.fixed_ibrav = false;