CI: wait and retry for diffile to exist

[siddharth-krishna]

An attempt at fixing #265

[github-actions]

Regression test results on commit 4f0635b

       Benchmark    Time (s)                 GDX Diff     Accuracy       Correct    Additional
----------------  ----------  -----------------------  -----------  ------------  ------------
   DemoS_001-all   3.1   3.9            OK         OK  100.0 100.0    118    118      3      3
   DemoS_002-all   3.3   3.5            OK         OK  100.0 100.0    344    344      3      3
   DemoS_003-all   3.7   4.0            OK         OK  100.0 100.0    633    633      6      6
       DemoS_004   3.8   4.9            OK         OK  100.0 100.0    662    662     12     12
      DemoS_004a   3.9   4.5            OK         OK  100.0 100.0    665    665     12     12
      DemoS_004b   3.8   4.9            OK         OK  100.0 100.0    665    665     12     12
   DemoS_004-all   4.0   4.7            OK         OK  100.0 100.0    667    667     12     12
   DemoS_005-all   4.4   5.5            13         13   99.7  99.7   1160   1160     12     12
   DemoS_006-all   5.0   6.0            13         13   99.7  99.7   1258   1258     12     12
   DemoS_007-all   5.9   6.9            13         13   99.8  99.8   2155   2155     12     12
DemoS_007-all-1r   5.1   6.4            11         11   99.8  99.8   1179   1179     12     12
   DemoS_008-all   7.9   9.0            13         13   99.9  99.9   5333   5333     18     18
   DemoS_009-all   8.6  10.2            26         26   99.9  99.9   5807   5807     29     29
   DemoS_010-all   8.8  10.5           822        822   88.4  88.4   6139   6139     29     29
   DemoS_011-all   8.9  10.2           854        854   88.0  88.0   6150   6150     29     29
   DemoS_012-all   9.2  10.7           901        901   88.2  88.2   6306   6306     53     53
DemoS_special-t1   4.8   6.0  Error runn… Error runn…   92.5  92.5   2110   2110     48     48
    TIMES-IE-all  25.6  27.2          3131       3131   97.5  97.5  42460  42460   2826   2826
    TIMES-IE-NoM  23.5  23.7           363        363   99.3  99.3  40528  40528    632    632
    TIMES-IE-MCB  23.9  24.4          1106       1106   97.6  97.6  42067  42067    632    632
    TIMES-NZ-KEA  34.6  34.7          3932       3932   98.3  98.3  76416  76416    458    458
    TIMES-NZ-TUI  24.8  24.9          3966       3966   98.3  98.3  76042  76042    474    474
 (__main__:MainThread:pid-5938 "/home/runner/work/xl2times/xl2times/xl2times/utils/run_benchmarks.py:394")
2025-01-27 18:53:14.477 | INFO     : Total runtime: 246.55s (main: 226.65s) (__main__:MainThread:pid-5938 "/home/runner/work/xl2times/xl2times/xl2times/utils/run_benchmarks.py:418")
2025-01-27 18:53:14.477 | INFO     : Change in runtime (negative == faster): +19.90s (+8.8%) (__main__:MainThread:pid-5938 "/home/runner/work/xl2times/xl2times/xl2times/utils/run_benchmarks.py:419")
2025-01-27 18:53:14.477 | INFO     : Change in correct rows (higher == better): +0 (+0.0%) (__main__:MainThread:pid-5938 "/home/runner/work/xl2times/xl2times/xl2times/utils/run_benchmarks.py:426")
2025-01-27 18:53:14.477 | INFO     : Change in additional rows: +0 (+0.0%) (__main__:MainThread:pid-5938 "/home/runner/work/xl2times/xl2times/xl2times/utils/run_benchmarks.py:433")
2025-01-27 18:53:14.477 | SUCCESS  : No regressions. You're awesome! (__main__:MainThread:pid-5938 "/home/runner/work/xl2times/xl2times/xl2times/utils/run_benchmarks.py:447")

This comment will be updated when new commits are added to the PR.