MBEDTLS_PSA_INJECT_ENTROPY: ignore seed file

The test framework leaves the seed file behind (like it does with the
corresponding file in the legacy API, namely seedfile), so ignore it.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/.gitignore b/.gitignore
index f2c4a3b..54b3c54 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,7 @@
 # Random seed file created by test scripts and sample programs
 seedfile
+# MBEDTLS_PSA_INJECT_ENTROPY seed file created by the test framework
+00000000ffffff52.psa_its
 
 # CMake build artifacts:
 CMakeCache.txt