docker: add tzdata package, to support TZ env variable

.github/workflows/Dockerfile.ci.alpine

@@ -86,7 +86,7 @@ RUN set -eux; \
 # verify that the binary works
 	gosu --version; \
 	gosu nobody true
-RUN apk add --no-cache tini ca-certificates bash && \
+RUN apk add --no-cache tini ca-certificates bash tzdata && \
     addgroup -g $GID $USER && \
     adduser \
     --disabled-password \

.github/workflows/Dockerfile.ci.debian

@@ -58,7 +58,7 @@ ENV UID=1000
 ENV GID=1000
 ENV USER=lldap
 RUN apt update && \
-    apt install -y --no-install-recommends tini openssl ca-certificates gosu && \
+    apt install -y --no-install-recommends tini openssl ca-certificates gosu tzdata && \
     apt clean && \
     rm -rf /var/lib/apt/lists/* && \
     groupadd -g $GID $USER && useradd --system -m -g $USER --uid $UID $USER && \