work around droid serif being de-listed from google fonts

See google/fonts issue number 1223

R/ggplot2.R

     xaringanthemer_env$showtext_auto <- TRUE
   }
 
-  if (family %in% theme_xaringan_get_value("registered_font_families") %||% "") {
+  if (family %in% xaringanthemer_env[["registered_font_families"]] %||% "") {
     return(family)
   }
 
   if (!requires_package(pkg = "sysfonts", fn, required = FALSE)) {
     return(family)
+  } else if (family == "Droid Serif") {
+    dstmp <- tempfile("droid-serif", fileext = "ttf")
+    download.file(
+      "https://github.com/google/fonts/raw/feb15862e0c66ec0e7531ca4c3ef2607071ea700/apache/droidserif/DroidSerif-Regular.ttf",
+      dstmp,
+      quiet = TRUE
+    )
+    sysfonts::font_add(
+      family = "Droid Serif",
+      regular = dstmp
+    )
   } else if (!family %in% sysfonts::font_families()) {
     is_default_font <- family %in% c(
       "Roboto",

tests/testthat/css/duo-header_bg.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/duo.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/duo_accent.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/duo_accent_inverse.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/mono_accent.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/mono_accent_inverse.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/mono_dark.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/mono_light-header_bg.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/mono_light.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/solarized_dark-header_bg.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/solarized_dark.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/solarized_light.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {

tests/testthat/css/xaringan.css

 }
 .remark-slide-content {
   background-color: var(--background-color);
-  font-size: var(--text-font-size);
   padding: 1rem 4rem 1rem 4rem;
 }
 .remark-slide-content h1 {