CI: update GITHUB_TOKEN variable's name to a new secret name

[lukaszstolarczuk]

ugh with these scripts 😞 ref. https://github.com/pmem/libpmemobj-cpp/runs/7518489401?check_suite_focus=true#step:4:11292

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This change is 

[codecov[bot]]

Codecov Report

Merging #1267 (f7c6ed4) into stable-1.9 (ddd2921) will decrease coverage by 56.83%. The diff coverage is n/a.

@@               Coverage Diff               @@
##           stable-1.9    #1267       +/-   ##
===============================================
- Coverage       88.54%   31.70%   -56.84%     
===============================================
  Files              40       39        -1     
  Lines            3806     1883     -1923     
===============================================
- Hits             3370      597     -2773     
- Misses            436     1286      +850     

Flag	Coverage Δ
tests_clang_debug_cpp17	31.70% <ø> (-0.96%)	:arrow_down:
tests_gcc_debug	?

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Impacted Files	Coverage Δ
include/libpmemobj++/pext.hpp	0.00% <0.00%> (-100.00%)	:arrow_down:
include/libpmemobj++/detail/pair.hpp	0.00% <0.00%> (-100.00%)	:arrow_down:
include/libpmemobj++/detail/pool_data.hpp	0.00% <0.00%> (-100.00%)	:arrow_down:
include/libpmemobj++/persistent_ptr_base.hpp	0.00% <0.00%> (-100.00%)	:arrow_down:
include/libpmemobj++/detail/make_atomic_impl.hpp	0.00% <0.00%> (-100.00%)	:arrow_down:
...pmemobj++/container/detail/contiguous_iterator.hpp	0.00% <0.00%> (-100.00%)	:arrow_down:
include/libpmemobj++/container/array.hpp	0.00% <0.00%> (-95.84%)	:arrow_down:
include/libpmemobj++/experimental/v.hpp	0.00% <0.00%> (-95.24%)	:arrow_down:
include/libpmemobj++/container/basic_string.hpp	0.00% <0.00%> (-95.11%)	:arrow_down:
include/libpmemobj++/container/vector.hpp	0.00% <0.00%> (-90.78%)	:arrow_down:
... and 28 more

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