build-unit-test-docker: Fix https_proxy

The https_proxy was not correctly set and if build with proxy settings,
it gives below error:

    base: WARNING: Retrying (Retry(total=4, connect=None, read=None,
    redirect=None, status=None)) after connection broken by
    'ProxyError('Cannot connect to proxy.',
    NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection
    object at 0x7efe419e99d0>: Failed to establish a new connection:
    [Errno -2] Name or service not known'))': /simple/inflection/
    RAN: /usr/bin/docker build --build-arg http_proxy=http://<myproxy>
    --build-arg 'https_proxy={https_proxy}' --network=host --force-rm
    --no-cache=false -t
    openbmc/ubuntu-unit-test-base:2021-W07-773f263e895d8ed6 -

Tested: Fix the https_proxy string and verify the CI passes.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I87f543d33747b4957af83990f80bd8e832f4e5e3
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 23541f1..38a4508 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -678,7 +678,7 @@
             "--build-arg",
             f"http_proxy={http_proxy}",
             "--build-arg",
-            "https_proxy={https_proxy}",
+            f"https_proxy={http_proxy}",
         ]
     )