chore: Fix checksum files

[suzuki-shunsuke]

This pull request fixes release.sh to resolve two issues of checksum files:

1. The checksum of ssm-darwin-arm64 is wrong due to typo
2. Remove the prefix release/ from checksum files to validate checksums by sha256sum -c

Now we can't validate checksums by cat *.sha | sha256sum -c due to the prefix release/.

$ cat *.sha | sha256sum -c
sha256sum: release/ssm-darwin-amd64: No such file or directory
release/ssm-darwin-amd64: FAILED open or read
sha256sum: release/ssm-darwin-amd64: No such file or directory
release/ssm-darwin-amd64: FAILED open or read
sha256sum: release/ssm-linux-amd64: No such file or directory
release/ssm-linux-amd64: FAILED open or read
sha256sum: WARNING: 3 listed files could not be read

---

Before:

$ cat *.sha
c23c58ab82cb2cf6b78577fc325a6d2ff577e09c5b2501c2593d2c991f955034  release/ssm-darwin-amd64
c23c58ab82cb2cf6b78577fc325a6d2ff577e09c5b2501c2593d2c991f955034  release/ssm-darwin-amd64
f2242ae9b75a3d112fcca5d7a435f5e239de70da3fbcc30d323c2d3f41c50990  release/ssm-linux-amd64

After:

$ cat *.sha
c23c58ab82cb2cf6b78577fc325a6d2ff577e09c5b2501c2593d2c991f955034  ssm-darwin-amd64
0903711c5da58c19c673c2a0edb70ec44f775affe47f4929a6e444462c352c1e  ssm-darwin-arm64
f2242ae9b75a3d112fcca5d7a435f5e239de70da3fbcc30d323c2d3f41c50990  ssm-linux-amd64

Test

I've confirmed release.sh works as expected:

$ bash release.sh 
+ rm -rf release
+ mkdir release
+ GOOS=darwin
+ GOARCH=amd64
+ go build -o release/ssm-darwin-amd64
go: downloading github.com/urfave/cli v1.22.10
go: downloading github.com/aws/aws-sdk-go-v2/config v1.27.15
go: downloading github.com/aws/aws-sdk-go-v2/service/ssm v1.50.3
go: downloading github.com/aws/aws-sdk-go-v2 v1.27.0
go: downloading github.com/aws/aws-sdk-go-v2/credentials v1.17.15
go: downloading github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.16.3
go: downloading github.com/aws/aws-sdk-go-v2/service/sso v1.20.8
go: downloading github.com/aws/aws-sdk-go-v2/service/ssooidc v1.24.2
go: downloading github.com/aws/aws-sdk-go-v2/service/sts v1.28.9
go: downloading github.com/aws/aws-sdk-go-v2/internal/configsources v1.3.7
go: downloading github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.6.7
go: downloading github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.11.9
+ GOOS=linux
+ GOARCH=amd64
+ go build -o release/ssm-linux-amd64
+ GOOS=darwin
+ GOARCH=arm64
+ go build -o release/ssm-darwin-arm64
+ cd release
+ sha256sum ssm-darwin-amd64
+ sha256sum ssm-darwin-amd64
+ sha256sum ssm-darwin-arm64

$ cd release 
$ ls
ssm-darwin-amd64      ssm-darwin-arm64      ssm-linux-amd64
ssm-darwin-amd64.sha  ssm-darwin-arm64.sha  ssm-linux-amd64.sha
$ cat *.sha | sha256sum -c
ssm-darwin-amd64: OK
ssm-darwin-arm64: OK
ssm-darwin-amd64: OK