[BUG] Error adding 2+ files after init --shared on Windows with fscache

[Steven Kelly <stevek@metacase.com>]

What did you do before the bug happened? (Steps to reproduce your issue)
Clean install of Git on Windows 10 using default options
git init --shared
echo x>x
echo y>y
git add -A

What did you expect to happen? (Expected behavior)
The two files are added with no errors

What happened instead? (Actual behavior)
error: unable to create temporary file: No such file or directory
error: y: failed to insert into database
error: unable to index file 'y'
fatal: adding files failed

What's different between what you expected and what actually happened?
The add command fails with an error 'unable to create temporary file'

Anything else you want to add:
If I omit --shared, there is no error
If there is only one file, there is no error
If the echo commands do not have characters, just adding a blank line, there is no error
If I turn off fscache, there is no error (git config --global core.fscache false)
All other filenames and contents also show the problem, for 2+ files
E.g. with files x,y,z,a,b, error happens on b - seems to be 2nd file in alphabetical order
The various GIT_TRACE_* options do not reveal anything useful, just normal setup up to trace: built-in: git add -A
Problem has existed for over a year (Google the 'unable to create...or directory' error and git)
Confirmed in git version 2.26.2.windows.1


Please review the rest of the bug report below.
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[System Info]
git version:
git version 2.30.2.windows.1
cpu: x86_64
built from commit: 37f0a4afad027cf030747a1ef45537ba86162960
sizeof-long: 4
sizeof-size_t: 8
shell-path: /bin/sh
uname: Windows 10.0 19041 
compiler info: gnuc: 10.2
libc info: no libc information available
$SHELL (typically, interactive shell): <unset>


[Enabled Hooks]
not run from a git repository - no hooks to show