Fix/ignore venv restrict bind mount (#1796)

* Ignore .venv files in git and docker

* Only bind mount cwd for `main`

Bind mounting `.` in every case would interfere with .dockerignore
We want to ignore `.venv` so that the venv of the built docker image
is used. Otherwise we would use the venv of the host inside docker.
This would negate the whole point of testing in a docker container.

Bind mounting `.` is however useful if one wants to use docker just
for "sandboxing" while running the tests on the local machine.

---------

Co-authored-by: intrigus <abc123zeus@live.de>

.dockerignore

@@ -0,0 +1,2 @@
+# venv
+.venv/

.gitignore

@@ -84,3 +84,6 @@ tests/qemu-tests/images
 
 .zig/
 gdb.txt
+
+# venv
+.venv/

docker-compose.yml

@@ -1,14 +1,16 @@
 version: "3.8"
 services:
-  main: &base-spec
+  base: &base-spec
     build: .
-    volumes:
-      - .:/pwndbg
     platform: linux/amd64
     security_opt:
       - seccomp:unconfined
     cap_add:
       - SYS_PTRACE
+  main:
+    <<: *base-spec
+    volumes:
+      - .:/pwndbg
 
   ubuntu18.04:
     <<: *base-spec