Ignore PhysicsServer3DExtension class in C#

PhysicsServer3DExtension inherits from PhysicsServer3D which is a
singleton class, since singleton classes are generated as static in C#
it would generate invalid C# so for now we'll be
ignoring PhysicsServer3DExtension.

.github/workflows/linux_builds.yml

@@ -18,16 +18,16 @@ jobs:
       fail-fast: false
       matrix:
         include:
-#          - name: Editor w/ Mono (target=release_debug, tools=yes, tests=yes)
-#            cache-name: linux-editor-mono
-#            target: release_debug
-#            tools: true
-#            tests: false # Disabled due freeze caused by mix Mono build and CI
-#            sconsflags: module_mono_enabled=yes mono_static=yes mono_glue=no
-#            doc-test: true
-#            bin: "./bin/godot.linuxbsd.opt.tools.64.mono"
-#            build-mono: true
-#            artifact: true
+          - name: Editor w/ Mono (target=release_debug, tools=yes, tests=yes)
+            cache-name: linux-editor-mono
+            target: release_debug
+            tools: true
+            tests: false # Disabled due freeze caused by mix Mono build and CI
+            sconsflags: module_mono_enabled=yes mono_static=yes mono_glue=no
+            doc-test: true
+            bin: "./bin/godot.linuxbsd.opt.tools.64.mono"
+            build-mono: true
+            artifact: true
 
           - name: Editor with doubles and sanitizers (target=debug, tools=yes, float=64, tests=yes, use_asan=yes, use_ubsan=yes)
             cache-name: linux-editor-double-sanitizers
@@ -42,14 +42,14 @@ jobs:
             # Skip 2GiB artifact speeding up action.
             artifact: false
 
-#          - name: Template w/ Mono (target=release, tools=no)
-#            cache-name: linux-template-mono
-#            target: release
-#            tools: false
-#            tests: false
-#            sconsflags: module_mono_enabled=yes mono_static=yes mono_glue=no debug_symbols=no
-#            build-mono: false
-#            artifact: true
+          - name: Template w/ Mono (target=release, tools=no)
+            cache-name: linux-template-mono
+            target: release
+            tools: false
+            tests: false
+            sconsflags: module_mono_enabled=yes mono_static=yes mono_glue=no debug_symbols=no
+            build-mono: false
+            artifact: true
 
           - name: Minimal Template (target=release, tools=no, everything disabled)
             cache-name: linux-template-minimal