INSTALL: Make note that Linux kernel 6.12.x or earlier is needed for reiserfs testing

Also, remove wording suggesting that tests may be skipped if prerequisites
are not installed. Tests should never be skipped because of an environment
misconfiguration, instead they should return a hard error (code 99).

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

INSTALL

@@ -66,7 +66,7 @@ More cross compiling toolchains can be found at the following trusted sites:
 * https://mirrors.kernel.org/pub/tools/crosstool/
 * https://toolchains.bootlin.com/
 
-Prerequisites for make-check:
+Prerequisites for running make-check successfully:
 
 * qemu, specifically the binary "qemu-system-ARCH" where ARCH is the
   architecture GRUB has been built for; the "qemu-system" package on Debian
@@ -86,6 +86,8 @@ Prerequisites for make-check:
     reiserfs, udf, xfs
   - On newer kernels, the exfat kernel modules may be used instead of the
     exfat FUSE filesystem
+  - Kernel version 6.12.x was the last series to include reiserfs support,
+    so later kernels will fail the reiser filesystem test.
 * The following are Debian named packages required mostly for the full
   suite of filesystem testing (but some are needed by other tests as well):
   - btrfs-progs, dosfstools, e2fsprogs, erofs-utils, exfatprogs, exfat-fuse,
@@ -96,8 +98,8 @@ Prerequisites for make-check:
   - attr, cpio, g++, gawk, parted, recode, tar, util-linux
 
 Note that `make check' will run and many tests may complete successfully
-with only a subset of these prerequisites. However, some tests may be
-skipped or fail due to missing prerequisites.
+with only a subset of these prerequisites. However, some tests may fail
+due to missing prerequisites.
 
 To build the documentation you'll need:
 * texinfo, for the info and html documentation