chore: Reduce dependabot frequency to weekly

[kylecarbs]

It was tiring seeing 5+ PRs a day for dependency updates.
Reducing this to a week should save some time!

[codecov]

Codecov Report

Merging #560 (e91f533) into main (d371a66) will increase coverage by 0.20%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #560      +/-   ##
==========================================
+ Coverage   63.05%   63.25%   +0.20%     
==========================================
  Files         194      194              
  Lines       11107    11107              
  Branches       85       85              
==========================================
+ Hits         7003     7026      +23     
+ Misses       3348     3329      -19     
+ Partials      756      752       -4     

Flag	Coverage Δ
unittest-go-	61.92% <ø> (+0.13%)	⬆️
unittest-go-macos-latest	57.60% <ø> (+0.02%)	⬆️
unittest-go-ubuntu-latest	60.89% <ø> (+0.04%)	⬆️
unittest-go-windows-2022	56.49% <ø> (+0.01%)	⬆️
unittest-js	63.32% <ø> (ø)

Impacted Files	Coverage Δ
provisionersdk/serve.go	35.13% <0.00%> (-8.11%)	⬇️
peer/channel.go	83.04% <0.00%> (-0.59%)	⬇️
provisionerd/provisionerd.go	80.81% <0.00%> (-0.33%)	⬇️
peer/conn.go	79.18% <0.00%> (-0.26%)	⬇️
cli/projectcreate.go	48.71% <0.00%> (+1.92%)	⬆️
coderd/provisionerdaemons.go	63.20% <0.00%> (+4.08%)	⬆️
database/db.go	65.51% <0.00%> (+10.34%)	⬆️

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