tests: Fix shellcheck issue SC2148 by adding a shell directive

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
diff --git a/tests/Makefile.am b/tests/Makefile.am
index f89fc10..4c601b8 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -238,8 +238,7 @@
 .PHONY: syntax-check
 syntax-check:
 # SC2009: Consider using pgrep instead of grepping ps output.
-# SC2148: Tips depend on target shell and yours is unknown. Add a shebang or a 'shell' directive.
-	shellcheck -e SC2009,SC2148 \
+	shellcheck -e SC2009 \
 		$(TESTS) $(TEST_UTILS) $(filter _test_%,$(EXTRA_DIST))
 
 check: check-am check-display
diff --git a/tests/load_vtpm_proxy b/tests/load_vtpm_proxy
index d192b69..823ccdf 100644
--- a/tests/load_vtpm_proxy
+++ b/tests/load_vtpm_proxy
@@ -1,4 +1,6 @@
 
+# shellcheck shell=bash
+
 # For the license, see the LICENSE file in the root directory.
 
 # Some distros may not have the device
diff --git a/tests/test_common b/tests/test_common
index 247cc9c..e0946ac 100644
--- a/tests/test_common
+++ b/tests/test_common
@@ -1,5 +1,6 @@
 
 # shellcheck disable=SC2043
+# shellcheck shell=bash
 # For the license, see the LICENSE file in the root directory.
 
 function wait_for_file()
diff --git a/tests/test_cuse b/tests/test_cuse
index 95f0fcc..3d84122 100644
--- a/tests/test_cuse
+++ b/tests/test_cuse
@@ -1,4 +1,6 @@
 
+# shellcheck shell=bash
+
 # For the license, see the LICENSE file in the root directory.
 
 if ! [[ "$(uname -s)" =~ Linux ]]; then