crypto/tests: do not use RP_FIXTURE_ENV for ossl_context_service tests

`ossl_context_service` only works if we have one seastar shard per
thread. RP_FIXTURE_ENV env variable disables the service to make it safe
to run multiple seastar shards in a single thread. A lot of tests need
this, so it is set by default. However, to test the service itself we
need to enable it.

src/v/crypto/tests/BUILD

@@ -168,7 +168,7 @@ redpanda_cc_gtest(
     cpu = 2,
     data = common_data_deps,
     defines = ["FIPS_MODULE_REQUIRED"],
-    env = common_env,
+    env = common_env | {"RP_FIXTURE_ENV": ""},
     deps = [
         ":crypto_test_utils",
         ":ossl_context_service_test_base",
@@ -192,7 +192,7 @@ redpanda_cc_gtest(
     cpu = 2,
     data = common_data_deps,
     defines = ["FIPS_MODULE_REQUIRED"],
-    env = common_env,
+    env = common_env | {"RP_FIXTURE_ENV": ""},
     deps = [
         ":crypto_test_utils",
         ":ossl_context_service_test_base",