fix TestClientOnResponseError parallel tests

[SVilgelm]

In case of using t.Parallel() inside a for loop, the loop variables must be copied, otherwise only the last test will be executed.

    for _, test := range tests {
        t.Run(test.name, func(t *testing.T) {
            t.Parallel()

changed to

    for _, test := range tests {
        test := test
        t.Run(test.name, func(t *testing.T) {
            t.Parallel()

also the AuthServer must be created within the test, otherwise some tests fail.

t.Log(test.Name) can be used to verify the issue:

    for _, test := range tests {
        t.Run(test.name, func(t *testing.T) {
            t.Parallel()
            t.Log("Test name:", test.name)

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +0.55% :tada:

Comparison is base (1ae2aac) 95.65% compared to head (b6a0e29) 96.21%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #710 +/- ## ========================================== + Coverage 95.65% 96.21% +0.55% ========================================== Files 12 12 Lines 1612 1612 ========================================== + Hits 1542 1551 +9 + Misses 42 38 -4 + Partials 28 23 -5 ``` [see 2 files with indirect coverage changes](https://app.codecov.io/gh/go-resty/resty/pull/710/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-resty)

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[SVilgelm]

I saw this issue so many times :)

[jeevatkm]

It would be helpful if go test throws some warning or error if it detects this case.