ci: Switch to ubuntu:26.04 images

Where possible, change to the latest Ubuntu release. The 32-bit images
still aren't bumped because of the time64 mismatch.

(backport <rust-lang#5215>)
(cherry picked from commit 836a774)

Author: tgross35

ci/docker/aarch64-linux-android/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN dpkg --add-architecture i386
 RUN apt-get update && apt-get install -y --no-install-recommends \

ci/docker/aarch64-unknown-linux-gnu/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates \

ci/docker/aarch64-unknown-linux-musl/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates \

ci/docker/arm-linux-androideabi/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN dpkg --add-architecture i386
 RUN apt-get update && apt-get install -y --no-install-recommends \

ci/docker/asmjs-unknown-emscripten/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 # This is a workaround to avoid the interaction with tzdata.
 ENV DEBIAN_FRONTEND=noninteractive

ci/docker/i686-linux-android/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN dpkg --add-architecture i386
 RUN apt-get update && apt-get install -y --no-install-recommends \

ci/docker/i686-unknown-linux-gnu/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         ca-certificates \

ci/docker/i686-unknown-linux-musl/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN dpkg --add-architecture i386 && \
     apt-get update && apt-get install -y --no-install-recommends \

ci/docker/loongarch64-unknown-linux-gnu/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates \

ci/docker/loongarch64-unknown-linux-musl/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:25.04
+FROM ubuntu:26.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates \