(ci) update github actions ci to use a single GO_VERSION variable

[ramin]

This sets a single variable (GO_VERSION) in the main ci.yml workflow, which will be the single place we set the current go version. We then run a setup job that sets an required output for subsequent jobs to use, adding:

with:
  go-version: ${{ needs.setup.outputs.go-version }}

Where we had previously either:

1. duplicated the GO_VERSION env var in that workflow
2. passed in 1.21 or whatever go version explicitly

When the rpc openrpc.json workflow check changes are merged, this will also prevent another duplication of the go version appearing.

refs #2698

[codecov-commenter]

Codecov Report

Merging #2806 (15b3f6d) into main (565691f) will increase coverage by 0.24%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2806      +/-   ##
==========================================
+ Coverage   51.57%   51.81%   +0.24%     
==========================================
  Files         167      167              
  Lines       10787    10787              
==========================================
+ Hits         5563     5589      +26     
+ Misses       4735     4706      -29     
- Partials      489      492       +3     

see 6 files with indirect coverage changes

[MSevey]

Nice! Beside not skipping for dependabot this lgtm.

This is a good workaround not having global env in the actions. The alternative would be to set a secret but then we can't actually see the version, so this is better.

cc @celestiaorg/devops for visibility and helping to reapply elsewhere.

[ramin]

had to resolve conflict on this