Only override the current project buffer-locally

* lisp/progmodes/project.el (project-switch-project): Only
override the current project buffer-locally.  This is mostly for
the the mode-line indicator (https://debbugs.gnu.org/66317#53).
1 job for master in 10 minutes and 36 seconds (queued for 1 minute and 13 seconds)
Status Job ID Name Coverage
  Normal
failed #76357
test-lisp-progmodes-inotify

00:10:36

 
Name Stage Failure
failed
test-lisp-progmodes-inotify Normal
Uploading artifacts for failed job
Uploading artifacts...
WARNING: test-lisp-progmodes-inotify-ffe894d0/: no matching files. Ensure that the artifact path is relative to the working directory
ERROR: No files to upload
Uploading artifacts...
WARNING: test-lisp-progmodes-inotify-ffe894d0/junit-test-report.xml: no matching files. Ensure that the artifact path is relative to the working directory
ERROR: No files to upload
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1