Build failures in self-tests on 32-bit platforms

[jas4711]

Hi. I got build failures on armel and armhf because the source codes uses too large integer values:

# github.com/tink-crypto/tink-go/internal/aead_test [github.com/tink-crypto/tink-go/internal/aead.test]
src/github.com/tink-crypto/tink-go/internal/aead/aesgcm_test.go:30:65: cannot use 1 << 60 (untyped int constant 1152921504606846976) as int value in argument to t.Errorf (overflows)
# github.com/tink-crypto/tink-go/signature/rsassapss_test [github.com/tink-crypto/tink-go/signature/rsassapss.test]
src/github.com/tink-crypto/tink-go/signature/rsassapss/key_test.go:57:22: cannot use 1 << 31 (untyped int constant 2147483648) as int value in struct literal (overflows)
# github.com/tink-crypto/tink-go/signature/rsassapkcs1_test [github.com/tink-crypto/tink-go/signature/rsassapkcs1.test]
src/github.com/tink-crypto/tink-go/signature/rsassapkcs1/key_test.go:53:21: cannot use 1 << 31 (untyped int constant 2147483648) as int value in struct literal (overflows)

Full log here: https://salsa.debian.org/jas/golang-github-tink-crypto-tink-go/-/jobs/7271759/viewer

Thanks,
/Simon