ci: add go vet to lint step

[manmartgarc]

• 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 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)

[jba]

Thanks!
If you're interested, you could look into those staticcheck hits.