Corrects tst_palette.cpp after merge of PR6019.

[njvdberg]

PR #6019 removed using namespace std; but PR #5760 introduced tst_palette.cpp which was created before the merge of PR #6019 and used vector>/code> without the std:: prefix.

Resolves: no issue

• I signed CLA
• I made sure the code in the PR follows the coding rules
• I made sure the code compiles on my machine
• I made sure there are no unnecessary changes in the code
• I made sure the title of the PR reflects the core meaning of the issue you are solving
• I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"
• [n.a.] I made sure the commit message title starts with "fix #424242:" if there is a related issue
• [n.a.] I created the test (mtest, vtest, script test) to verify the changes I made

[Spire42]

Ack. Thanks for the fix.

[njvdberg]

@Spire42 Nothing you could do about it, the 2 PR's just crossed.
And I had to correct it because my local test failed :-)