E2E tests use functions not yet available in go 1.18

[avinal]

Expected Behavior

E2E tests should compile and pass when using go 1.18.x

Actual Behavior

The tests fail to compile because it uses one function that is not available in go 1.18. Refer:

https://github.com/tektoncd/results/blob/fdc47542cc0ce52fadaa4389a01ff0c2b75fe6e5/test/e2e/client/rest.go#L117

# github.com/tektoncd/results/test/e2e/client
client/rest.go:117:13: c.url.JoinPath undefined (type *url.URL has no field or method JoinPath)
FAIL    github.com/tektoncd/results/test/e2e [build failed]

Go mod file:

https://github.com/tektoncd/results/blob/fdc47542cc0ce52fadaa4389a01ff0c2b75fe6e5/go.mod#L3

Minimum go version required for this function is 1.19

Steps to Reproduce the Problem

1. Pull the latest commit
2. Run go version. It should be 1.18.x
3. Run ./test/e2e-tests.sh
4. See the error

Additional Info

• Refer: net/url package documentation for go1.18.10
• Refer: net/url package documentation for go1.19

[avinal]

/assign