Adjust automation re: `make_v2021_runoff_file`

[douglatornell]

We need to ensure that make_v202111_runoff_file runs after all the river discharge observations have been collected. This PR implements a practical solution of launching make_runoff_file and make_v2021_runoff_file after make_ssh_files. We're forced into this solution because the race condition handling can't deal with ensuring that multiple instances of the same worker (collect_river_data) have completed.

[codecov[bot]]

Codecov Report

Merging #185 (2370597) into main (f33044b) will decrease coverage by 0.02%. The diff coverage is 63.63%.

:exclamation: Current head 2370597 differs from pull request most recent head 1ce88b7. Consider uploading reports for the commit 1ce88b7 to get more accurate results

@@            Coverage Diff             @@
##             main     #185      +/-   ##
==========================================
- Coverage   77.42%   77.41%   -0.02%     
==========================================
  Files         133      133              
  Lines       18491    18481      -10     
  Branches     1952     1953       +1     
==========================================
- Hits        14317    14307      -10     
  Misses       4119     4119              
  Partials       55       55              

Flag	Coverage Δ
unittests	77.41% <63.63%> (-0.02%)	:arrow_down:

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Impacted Files	Coverage Δ
nowcast/daily_river_flows.py	82.18% <0.00%> (ø)
nowcast/workers/make_runoff_file.py	28.45% <0.00%> (ø)
nowcast/next_workers.py	98.00% <100.00%> (ø)
tests/test_next_workers.py	99.74% <100.00%> (-0.01%)	:arrow_down:

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