msys2-runtime-3.5: branch off of msys2-runtime

Cygwin v3.5.0 has been released end of January 2024, and we were _about_
to be on the brink to switch to MSYS2 runtime based on the Cygwin
runtime v3.5.x.

However:

- That would leave Windows 7/8 compatibility behind.
- There have been a couple of hiccups in our testing, which led us to
  skip v3.5.0 already.
- We determined that a safer way would be to let users opt into using
  v3.5.x first, kicking the tires, so to say.

So let's establish a `msys2-runtime-3.5` package (much like
`msys2-runtime-3.3`) to be able to easily revert to a known state really
quickly, including the ability to run on Windows 7.

For now, this is merely a verbatim copy of the files in `msys2-runtime`,
and the next commits will modify them to reflect the version bump.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

.ci/ci-dont-install-list.txt

@@ -1,3 +1,4 @@
 msys2-runtime
 msys2-runtime-3.3
+msys2-runtime-3.5
 bash

msys2-runtime-3.3/PKGBUILD

@@ -4,7 +4,7 @@
 pkgbase=msys2-runtime-3.3
 pkgname=('msys2-runtime-3.3' 'msys2-runtime-3.3-devel')
 pkgver=3.3.6
-pkgrel=8
+pkgrel=9
 pkgdesc="Cygwin POSIX emulation engine"
 arch=('i686' 'x86_64')
 url="https://www.cygwin.com/"
@@ -279,7 +279,7 @@ package_msys2-runtime-3.3() {
   pkgdesc="Posix emulation engine for Windows"
   options=('!strip')
   provides=("msys2-runtime=${pkgver}")
-  conflicts=('catgets' 'libcatgets' 'msys2-runtime')
+  conflicts=('catgets' 'libcatgets' 'msys2-runtime' 'msys2-runtime-3.5')
   replaces=('catgets' 'libcatgets')
 
   mkdir -p "${pkgdir}"/usr
@@ -298,7 +298,7 @@ package_msys2-runtime-3.3-devel() {
   depends=("msys2-runtime-3.3=${pkgver}")
   provides=("msys2-runtime-devel=${pkgver}")
   options=('staticlibs' '!strip')
-  conflicts=('libcatgets-devel' 'msys2-runtime-devel')
+  conflicts=('libcatgets-devel' 'msys2-runtime-devel' 'msys2-runtime-3.5-devel')
   replaces=('libcatgets-devel')
 
   mkdir -p "${pkgdir}"/usr/bin