Documentation/dev-tools: use code-block with proper language

Now that we don't have automatic syntax highlighting, use the code-block
directive with the explicitly selected language, where appropriate.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Documentation/dev-tools/gcov.rst

@@ -201,7 +201,9 @@ Appendix A: gather_on_build.sh
 ------------------------------
 
 Sample script to gather coverage meta files on the build machine
-(see 6a)::
+(see 6a):
+
+.. code-block:: sh
 
     #!/bin/bash
 
@@ -232,7 +234,9 @@ Appendix B: gather_on_test.sh
 -----------------------------
 
 Sample script to gather coverage data files on the test machine
-(see 6b)::
+(see 6b):
+
+.. code-block:: sh
 
     #!/bin/bash -e