Define PIP_VERSION arg once it's needed

By defining it early we're busting the cache on pip version upgrade,
effectively making the split into two layers pointless.

Author: sairon

python/3.12/Dockerfile

@@ -3,7 +3,6 @@ FROM $BUILD_FROM
 
 ARG \
     PYTHON_VERSION \
-    PIP_VERSION \
     CERT_IDENTITY \
     CERT_OIDC_ISSUER \
     QEMU_CPU
@@ -110,6 +109,8 @@ RUN \
     && ln -s python3 python \
     && ln -s python3-config python-config
 
+ARG PIP_VERSION
+
 RUN set -ex; \
     \
     apk add --no-cache --virtual .fetch-deps openssl; \

python/3.13/Dockerfile

@@ -3,7 +3,6 @@ FROM $BUILD_FROM
 
 ARG \
     PYTHON_VERSION \
-    PIP_VERSION \
     CERT_IDENTITY \
     CERT_OIDC_ISSUER \
     QEMU_CPU
@@ -110,6 +109,8 @@ RUN \
     && ln -s python3 python \
     && ln -s python3-config python-config
 
+ARG PIP_VERSION
+
 RUN set -ex; \
     \
     apk add --no-cache --virtual .fetch-deps openssl; \

python/3.14/Dockerfile

@@ -3,7 +3,6 @@ FROM $BUILD_FROM
 
 ARG \
     PYTHON_VERSION \
-    PIP_VERSION \
     CERT_IDENTITY \
     CERT_OIDC_ISSUER \
     QEMU_CPU
@@ -111,6 +110,8 @@ RUN \
     && ln -s python3 python \
     && ln -s python3-config python-config
 
+ARG PIP_VERSION
+
 RUN set -ex; \
     \
     apk add --no-cache --virtual .fetch-deps openssl; \