tox: Add gbulb to test matrix

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 ; py3.7 runs into aiocoap unrelated trouble in setups on Debian sid, leaving
 ; this to `setup.py test` for now
-envlist = {py37,py38,py39,py310,py311,py312,pypy3}-{noextras,allextras},py311-uvloop,py311-uvloop-simpleudp,pypy3-simpleudp
+envlist = {py37,py38,py39,py310,py311,py312,pypy3}-{noextras,allextras},py311-uvloop,py311-gbulb,py311-uvloop-simpleudp,pypy3-simpleudp
 skip_missing_interpreters = true
 
 [testenv]
@@ -30,6 +30,12 @@ extras =
 setenv =
     AIOCOAP_DEFAULTS_EXPECT_ALL=1
 
+; Not running the non-default loops everywhere to save some CI time
+;
+; While it's perfectly realistic that older Python versions struggle with
+; those, that's likely more that loop's fault (or the fault of the test setup)
+; than aiocoap's.
+
 [testenv:py311-uvloop]
 description = Running on uvloop
 deps =
@@ -41,6 +47,17 @@ extras =
 setenv =
     AIOCOAP_TESTS_LOOP=uvloop
 
+[testenv:py311-gbulb]
+description = Running on gbulb
+deps =
+    coverage
+    pytest
+    gbulb
+extras =
+    all
+setenv =
+    AIOCOAP_TESTS_LOOP=gbulb
+
 ; Not running the -simple versions everywhere to save some CI time.
 ;
 ; For the CPython part we're using the uvloop runner, because AFAIR there were