Bump virtualenv from 20.4.2 to 20.4.3 in /docker/build_scripts (#1048)

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.4.2 to 20.4.3.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.4.2...20.4.3)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

docker/build_scripts/requirements.txt

@@ -82,9 +82,9 @@ appdirs==1.4.4; python_version=='2.7' \
 configparser==4.0.2; python_version=='2.7' \
     --hash=sha256:254c1d9c79f60c45dfde850850883d5aaa7f19a23f13561243a050d5a7c3fe4c \
     --hash=sha256:c7d282687a5308319bf3d2e7706e575c635b0a470342641c93bea0ea3b5331df
-virtualenv==20.4.2; python_version=='2.7' \
-    --hash=sha256:147b43894e51dd6bba882cf9c282447f780e2251cd35172403745fc381a0a80d \
-    --hash=sha256:2be72df684b74df0ea47679a7df93fd0e04e72520022c57b479d8f881485dbe3
+virtualenv==20.4.3; python_version=='2.7' \
+    --hash=sha256:83f95875d382c7abafe06bd2a4cdd1b363e1bb77e02f155ebe8ac082a916b37c \
+    --hash=sha256:49ec4eb4c224c6f7dd81bb6d0a28a09ecae5894f4e593c89b0db0885f565a107
 contextlib2==0.6.0.post1; python_version=='2.7' \
     --hash=sha256:01f490098c18b19d2bd5bb5dc445b2054d2fa97f09a4280ba2c5f3c394c8162e \
     --hash=sha256:3355078a159fbb44ee60ea80abd0d87b80b78c248643b49aa6d94673b413609b