[4.3] CI: Fix GitHub Action workflows

[aaronfranke]

This PR fixes several problems that occur on the GitHub Actions CI checks when compiling the 4.3 branch.

Note: I am aware that the Godot maintainers have told me to stop touching old Godot branches. However, I believe "making it compile" should still be in the scope of support (so, basically zero support, but not quite zero). See also PRs #121604 and #121603 for fixing the 4.4 and 4.5 branches.

Namely, it cherry-picks the following commits and PRs:

• PR CI: Update outdated GitHub Actions versions #115132 commit 30cfb06
  • Note: I included a further manual tweak to bump to v7 instead of just bumping to v6.
  • Avoids warnings from GitHub Actions itself.
• PR Build: Update to Xcode 26.0.1 for Apple builds #111799 commit fe6763c.
  • Required to fix compatibility with macos-latest.
• PR CI: Bump JavaScript actions to Node 24 #117428 commit 423ba3d
  • Avoids warnings from GitHub Actions itself.
• PR CI: Bump SCons version [4.10.0→4.10.1] #113403 commit a998842
  • This is actually a combination of several "bump SCons version" PRs by @Repiteo, but I'm only crediting the last one.
  • Required to fix compatibility with windows-latest and MSVC for Visual Studio 2026.
• New commit: "[4.3] Remove final from ICU4C UnicodeSet class"
  • Required to fix a warning in Clang: -Wunnecessary-virtual-specifier
  • This isn't cherry-picked from anything, since it only affects old versions of ICU4C. Newer Godot versions have a different fix: updating ICU4C to a newer release that fixes this warning.
• PR Fix more MSVC warnings for potential mod by 0 (C4724) #121746
  • Required to fix compiling with MSVC with werror=yes.
• PR Use explicit public access modifier in C# code #108885
  • Required to fix diffs when running the dotnet format step in pre-commit run --all-files.
  • I also included the doc comments that exist in newer Godot versions, since it's a harmless addition.

[Repiteo]

I was aiming for a more isolated implementation in those two PRs, but looking at how this was laid out, I think I prefer the more involved approach. Will go back and re-apply this format to those shortly

[akien-mga]

Looks good to me, thanks for doing this update for old branches.

[Repiteo]

Thanks!