build: update to Go 1.21.5

[jrasell]

No description provided.

[shoenig]

not related to this PR, but there is something very broken going on in the tests

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x49 pc=0x108110b]

goroutine 197 [running]:
github.com/hashicorp/nomad-driver-podman.(*Driver).StartTask(0xc0005d6000, 0xc0008582c0)
	/home/runner/work/nomad-driver-podman/nomad-driver-podman/driver.go:405 +0x6b
github.com/hashicorp/nomad/plugins/drivers.(*driverPluginServer).StartTask(0xc00051e648, {0xc0003f3170?, 0x5793e6?}, 0x0?)
	/home/runner/go/pkg/mod/github.com/hashicorp/[email protected]/plugins/drivers/server.go:111 +0x4c
github.com/hashicorp/nomad/plugins/drivers/proto._Driver_StartTask_Handler({0x1320140?, 0xc00051e648}, {0x15a37f0, 0xc0003f2c30}, 0xc00037ac40, 0x0)
	/home/runner/go/pkg/mod/github.com/hashicorp/[email protected]/plugins/drivers/proto/driver.pb.go:4502 +0x169
google.golang.org/grpc.(*Server).processUnaryRPC(0xc000568000, {0x15ac9a0, 0xc0005d56c0}, 0xc000864000, 0xc00056a4b0, 0x1e6d5e8, 0x0)
	/home/runner/go/pkg/mod/google.golang.org/[email protected]/server.go:1335 +0xde7
google.golang.org/grpc.(*Server).handleStream(0xc000568000, {0x15ac9a0, 0xc0005d56c0}, 0xc000864000, 0x0)
	/home/runner/go/pkg/mod/google.golang.org/[email protected]/server.go:1712 +0x9e7
google.golang.org/grpc.(*Server).serveStreams.func1.1()
	/home/runner/go/pkg/mod/google.golang.org/[email protected]/server.go:947 +0xbb
created by google.golang.org/grpc.(*Server).serveStreams.func1 in goroutine 118
	/home/runner/go/pkg/mod/google.golang.org/[email protected]/server.go:958 +0x145
FAIL TestPodmanDriver_Ports_MissingDriverConfig (-1.00s)