Add scrcpy-server to .gitignore

The script install_release.sh downloads a file named scrcpy-server to
the repo root directory. Add it to .gitignore so that it is ignored.

PR #4364 <https://github.com/Genymobile/scrcpy/pull/4364>

Signed-off-by: Romain Vimont <rom@rom1v.com>

.gitignore

@@ -7,3 +7,4 @@ build/
 .gradle/
 /x/
 local.properties
+/scrcpy-server