ci: remove monthly snapshots

[thehowl]

a latest "dev" tag was published, when it shouldn't have been: https://github.com/gnolang/gno/releases/tag/v0.0.1-dev.2024.06.01

this PR removes the monthly snapshots CI in favour of nightlies and normal releases.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.46%. Comparing base (0ee8bdc) to head (7e46b1b).
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2263      +/-   ##
==========================================
+ Coverage   49.94%   54.46%   +4.51%     
==========================================
  Files         578      578              
  Lines       77864    78865    +1001     
==========================================
+ Hits        38893    42952    +4059     
+ Misses      35847    32685    -3162     
- Partials     3124     3228     +104     

Flag	Coverage Δ
contribs/gnodev	24.24% <ø> (ø)
contribs/gnofaucet	15.31% <ø> (ø)
contribs/gnokeykc	0.00% <ø> (ø)
contribs/gnomd	0.00% <ø> (ø)
gno.land	61.64% <ø> (-0.03%)	⬇️
gnovm	59.99% <ø> (+14.91%)	⬆️
misc/autocounterd	0.00% <ø> (ø)
misc/genproto	0.00% <ø> (ø)
misc/genstd	73.90% <ø> (ø)
misc/goscan	0.00% <ø> (ø)
misc/logos	17.68% <ø> (+0.30%)	⬆️
misc/loop	0.00% <ø> (ø)
tm2	54.47% <ø> (-0.01%)	⬇️

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