GH-50537: [R] Fix vector_logic_linter warning by using && in if condition

[hiroyuki-sato]

Rationale for this change

Fix a vector_logic_linter warning by using && instead of & in an if condition.

Error: Not lint free
R/dplyr-funcs-datetime.R:541:26: warning: [vector_logic_linter] Use `&&` in conditional expressions.
      if (format == "%X" & tolower(Sys.info()[["sysname"]]) == "windows") {

https://github.com/apache/arrow/actions/runs/29632093671/job/88047704304?pr=50536#step:5:76

What changes are included in this PR?

• Replace & with && in the if condition.

Are these changes tested?

Yes.

Are there any user-facing changes?

No.

• GitHub Issue: [R] R/dplyr-funcs-datetime.R:541:26: warning: [vector_logic_linter] Use && in conditional expressions. #50537

[github-actions]

⚠️ GitHub issue #50537 has been automatically assigned in GitHub to PR creator.

[hiroyuki-sato]

I opened a PR for the R changes, but I’m not very familiar with R. I’d appreciate it if someone with R experience could take a look.

[thisisnic]

Looks like an update to the lintr package added a new linter a couple of days ago causing this to fail; this fix is spot on, thanks!