docs: Fix Contributing.md

docs/markdown/Contributing.md

@@ -174,7 +174,7 @@ contents of an additional file into the CI log on failure.
 Projects needed by unit tests are in the `test cases/unit`
 subdirectory. They are not run as part of `./run_project_tests.py`.
 
-#### Configuring project tests
+### Configuring project tests
 
 The (optional) `test.json` file, in the root of a test case, is used
 for configuring the test. All of the following root entries in the `test.json`
@@ -213,13 +213,13 @@ Exanple `test.json`:
 }
 ```
 
-##### env
+#### env
 
 The `env` key contains a dictionary which specifies additional
 environment variables to be set during the configure step of the test. `@ROOT@`
 is replaced with the absolute path of the source directory.
 
-##### installed
+#### installed
 
 The `installed` dict contains a list of dicts, describing which files are expected
 to be installed. Each dict contains the following keys:
@@ -277,7 +277,7 @@ the platform matches. The following values for `platform` are currently supporte
 | `cygwin`   | Matches when the platform is cygwin                                  |
 | `!cygwin`  | Not `cygwin`                                                         |
 
-##### matrix
+#### matrix
 
 The `matrix` section can be used to define a test matrix to run project tests
 with different meson options.
@@ -318,7 +318,7 @@ The above example will produce the following matrix entries:
 - `opt1=qwert`
 - `opt1=qwert opt2=true`
 
-##### do_not_set_opts
+#### do_not_set_opts
 
 Currently supported values are:
 - `prefix`