- Adds `go vet` call to the lint step in GA workflow.
- Enforces a compatible `go-version` with the minimum in the matrix for
the `test` step.
- Fixes some minor `.yml` formatting
Fixes#281
---
There's some discussion in #281 about adding
[staticcheck](https://staticcheck.dev/docs/) as well but when I ran it,
it found some hits (see below) that are presumably not severe, and I
wouldn't want to block deployments before getting some feedback from
maintainers.
```
internal/jsonrpc2/conn.go:695:4: this value of writeErr is never used (SA4006)
internal/jsonrpc2/conn.go:697:5: this value of err is never used (SA4006)
internal/jsonrpc2/conn.go:700:4: this value of err is never used (SA4006)
mcp/mcp_test.go:501:2: var resource3 is unused (U1000)
mcp/mcp_test.go:509:5: var embeddedResources is unused (U1000)
mcp/mcp_test.go:513:6: func handleEmbeddedResource is unused (U1000)
mcp/streamable.go:124:3: unnecessary assignment to the blank identifier (S1005)
mcp/streamable.go:291:2: field lastStreamID is unused (U1000)
mcp/streamable.go:293:2: field opts is unused (U1000)
mcp/streamable_test.go:542:29: argument ctx is overwritten before first use (SA4009)
```
This CL makes the following changes to our Github workflows, motivated
by #227:
- Add -race tests.
- Add go1.25rc2 to the build matrix.
- Check out code before setting up Go, so that the setup step can use
dependency caching.
